Edexcel IGCSE Physics Revision Notes PDF

IGCSE Physics (9-1) Revision Note Shawon Ibn Kamal Revised by: Anjuhan Saravana Raditu Roufir Page intentionally kept blank. Tables of Content Section 1: Forces and motion 5 a) Units 5 b) Movemen...

IGCSE Physics (9-1) Revision Note Shawon Ibn Kamal Revised by: Anjuhan Saravana Raditu Roufir Page intentionally kept blank. Tables of Content Section 1: Forces and motion 5 a) Units 5 b) Movement and Position 5 c) Forces, movement, shape and momentum 22 Section 2: Electricity 57 a) Units 57 b) Mains electricity 57 Section 3: Waves 80 a) Units 80 b) Properties of waves 80 c) The electromagnetic spectrum 86 d) Light and sound 89 Section 4: Energy resources and energy transfer 109 a) Units 109 b) Energy transfer 109 c) Work and power 115 d) Energy resources and electricity generation 117 Section 5: Solids, liquids and gases 120 a) Units 120 b) Density and pressure 120 c) Change of state 123 d) Ideal gas molecules 125 Section 6: Magnetism and electromagnetism 129 a) Units 129 b) Magnetism 129 c) Electromagnetism 132 Section 7: Radioactivity and particles 141 a) Units 141 b) Radioactivity 141 c) Fission and Fusion 152 Section 8: Astrophysics 153 (a) Units 153 (b) Motion in the universe 153  (c) Stellar evolution 153 (d) Cosmology 153 Appendix 1: Electrical circuit symbols 155 Appendix 2: Physical units 156 Appendix 3: Prefixes 157 Appendix 4: Formulae and Relationships 158 Appendix 5: Glossary (131) 159  Section 1: Forces and motion a) Units 1.1 use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s), newton per kilogram (N/kg), kilogram metre/second (kg m/s). Unit of mass=Kilogram (kg) Unit of distance=Metre (m) Unit of speed or velocity= Metre per second (m/s) Unit of acceleration= metre per second​2 ​(m/s​2​) Unit of Force= Newton(N) Unit of Time= Second(s) Unit of gravitational acceleration= Newton per kilogram(N/kg) Unit of Momentum= kilogram metre per second (kg m/s) b) Movement and Position 1.2 plot and interpret distance-time graphs Distance = ​The change of position of an object is called distance. The diagram shows an example: Figure 1 shows an object changes its position from A to B. So the distance travelled by the object is AB. Displacement = ​The change of position of an object in a particular direction is called displacement. Figure 2 shows another object changes its position from C to D through curved path but the displacement will be straight distance from C to D. Distance-time graph A distance-time graph represents the speed or velocity of any object. In this graph the object is moving at 1 m per second. It is in a constant speed. In a distance-time graph, distance should go to the Y-axis while time should go over the X-axis. Speed= gradient=distance/time = 3m/3s= 1m/s Few points that should be noted: 1. In a displacement – time graph or distance- time graph, the average velocity is found by the ratio △s △t where △s = change in displacement/distance and △t = time interval 2. A positive gradient of the displacement-time graph indicates that the car is moving in the same direction as the displacement. 3. A negative gradient of the displacement-time graph indicates that the car is moving in the opposite direction to the displacement. 4. A zero gradient of the displacement-time curve shows that the car is stationary. Some explanation of motion from graph: Zero displacement Constant displacement Not moving Acceleration Deceleration 1.3 know and use the relationship between average speed, distance moved and time: average speed = distance moved /time taken Speed: Speed is defined as the rate of change of distance. In other words, speed is the distance moved per unit time. It tells us how fast or slow an object is moving. Most objects or bodies do not move at constant speed. For example, the MRT train starts from rest at a station, moves faster and faster until it reaches a constant speed and then slows down to a stop at the next station. It is therefore more useful to define average speed rather than the actual speed. Average speed: Average speed is the total distance moved divided by total time taken. If you see the graph in 1.2 it had an average speed of 1 m/s. This is the relation between speed and distance,time. Distance and time has no relation individually. They are both different types of values. Instantaneous speed: The speed of an object at a particular moment is called instantaneous speed. It is measured by taking ratio of distance travelled by shortest possible time. Difference between speed and velocity: Speed Velocity i. The rate of distance travelled is speed. i. The rate of displacement travelled is velocity. ii. Speed can be in any direction. ii. Velocity is speed in particular direction. iii. Speed is a scalar quantity. iii. Velocity is a vector quantity. 1.4 describe experiments to investigate the motion of everyday objects such as toy cars or tennis balls Experiment:​Measuring speed using click and stopwatch Suppose you want to find the speed of cars driving down your road. You may have seen the police using speed guns to check that drivers are keeping to the speed limit. Speed guns use microprocessors to produce an instant reading of the speed of a moving vehicle, but you can conduct a very simple experiment to measure car speed. Measure the distance between two points along a straight section of road with a tape measure or “click” wheel. Use a stopwatch to measure the time taken for a car to travel the measured distance. Use the speed, distance and time equation to work out the speed of the car. Experiment​: Measuring speed using light gate method 1. Attach a cart of measured length centrally to the top of the toy car. 2. Air track ensures a frictionless way for the toy car. 3. A gentle push can move the toy car at a steady speed. 4. Arrange for the card to block a light gates beam as it passes through it. 5. Electronic timer measures how long the card takes to pass through the beam. 6. Now calculate the toy car's average velocity as it passes the light gate by: length of the card v= interuption time Experiment​: Measuring speed using ticker-time method Experiment​: Video (sequence) method – Measuring the velocity of a tennis ball. A tennis ball is let to move on a track at a steady speed. During the ball moves, video the ball moving along in front of calibrated scale (a scale where there is marking in length) attached to the slope. Play the video back to get the snap shots taken at a time. Measure how far the ball advances between snaps from the scale. The video camera can take 25 snaps each second. So the time between each snap is 0.04 second. Now calculate the balls average velocity between snaps using the following equation: ​ ​0.04 Velocity = distance moved between snaps ÷ Experiment​: To find out Average Speed of Toy car or trolley Apparatus: ​Toy car or tennis ball, meter rule, slotted masses, stopwatch, thread. Procedure: 1. Put toy car on bench and attach pulley to the corner of the bench as shown in figure. 2. Attach one end of the thread with toy car and other end with slotted masses while hanging them over pulley. 3. Keep toy car & pulley one meter apart with meter rule. 4. Hold the toy with hand so that it remains there immovable. 5. Time stop watch when you let toy to move a meter distance. 6. Repeat this & record reading for different distances in the following chart. 7. Draw graph to find out average speed, which can be found by finding the gradient of the graph. Precautions: 1. Do not hang heavier masses as this may break the thread. 2. Wear shoes as to avoid injury to foot in case of broken thread and fall of mass. 3. Put something soft under the hanging mass, like tray filled with sand. Sources of error: 1. Reaction time 2. Ruler may not be straight 3. Parallax error 4. Friction in the bench. Ways to improve: 1. Bench should be very polished friction. 2. Tyres of the toy should not be very rough. 3. Use light-gates instead of the stopwatch and connect light-gates to datalogger and then to computer, to get more accurate results. Experiment​: Measuring acceleration using light gate method  A card is mounted on the top of a trolley. The length of the card is measured. One light is set at the top of the track and the second one is at the end of the track. The trolley is given a gentle push to move through the track. When the trolley passes through the first light gate the electronic timer measures the t​1 to ​ cross the length of the card. So the velocity at the position of first light gate is measured by velocity. o V1​ = ​ length of the first card ​÷​t​1 During passing the second light gate, if the time measured by electronic timer is t2 then thevelocity can be measured by: o V2​ ​ = length of the second card ​÷​t​2 The time t​3​ is measured for the trolley to travel from first light gate to the second light gate by using a stopwatch. Now acceleration is = ​velocity difference​÷​t​3 = {(​length of the first card ​÷​t1​ ​)-(​length of the second card ​÷​t​2)}÷​ ​ t​3 Experiment​:Measuring acceleration using Video (sequence) method Experiment​: Measuring acceleration using Modern Version of Galileo’s Experiment: Apparatus - Light gate Interrupter Air pumper Air track Data logger or electronic timer Diagram – Working Procedure - We can measure the acceleration by conducting an experiment using an air-track which can be referred as the modern-version of Galileo experiment. From the diagram show the investigation where we can see that the air-track reduces friction because the glider rides on a cushion of air that is pumped continuously through holes along the air track. As the glider accelerates down the sloping track the white card mounted on it breaks a light beam, and the time the glider takes to pass is measured electronically. If the length of the card is measured, and this is entered into the spreadsheet, the velocity of the glider can be calculated by the spreadsheet programme using v = d/t. Observation - Here from the above procedure it is observed that the distance travelled in equal intervals is increased and that the rate of increase of speed is steady or uniform i.e. it is uniform acceleration. Table and Graph Conclusion The gradient of a velocity-time graph gives the acceleration Experiment​:Measuring acceleration using double light gate. 1. A card is mounted on the top of a trolley. 2. The length of the card is measured. 3. One light gate is at the top of the track and another light gate is at the end of the track. 4. The trolley is given a gentle push to move through the track. 5. When the trolley passes through the first light gate, the electronic timer measure the time (t​1​) to cross the length of the cord. 6. So the velocity at the position of first light gate is measured by: length of the cord v elocity, v 1 = t2 7. The time, t​3​ is measured for the trolley to travel from first light gate to 2​nd​ light gate by using a stopwatch. velocity dif f erence 8. Now, acceleration = t3 length of card length of card t2 − t1 = t3 Experiment​: Measuring acceleration using ticker tape. Apparatus: ​Ticker timer and tape, a.c. power supply, trolley, runway Procedure: 1. Set up the apparatus as in the diagram. 2. Connect the ticker timer to a suitable low-voltage power supply. 3. Allow the trolley to roll down the runway. 4. The trolley is accelerating as the distance between the spots is increasing. 5. The time interval between two adjacent dots is 0.02 s, assuming the ticker timer mars fifty dots per second. 6. Mark out five adjacent spaces near the beginning of the tape. Measure the length s1. 7. The time t1 is 5 × 0.02 = 0.1 s. 8. We can assume that the trolley was travelling at constant velocity for a small time interval. Thus initial velocity u = distance/time = s1/t1 9. Similarly mark out five adjacent spaces near the end of the tape and find the final velocity v. 10. Measure the distance s in metres from the centre point of u to the centre point of v. 11. The acceleration is found using the formula: v2 = u2 + 2as or a = v2 – u2 / 2t 12. By changing the tilt of the runway different values of acceleration are obtained. Repeat a number of times. 13. Tabulate results as shown. 1.5 know and use the relationship between acceleration, velocity and time: Acceleration is the rate at which objects change their velocity. The rate of decease of velocity is called deceleration. It is just a negative acceleration. It is defined as follows: Acceleration=change in velocity/time taken or (final velocity-initial velocity) /time taken This is written as an equation: v−u a = t where a=acceleration, v=final velocity, u=initial velocity and t=time 1.6 plot and interpret velocity-time graphs Velocity-time graphs represent the acceleration of any object. Velocity(m/s) is in the Y-axis while Time is the X-axis. Some common velocity-time graphs: 1.7 determine acceleration from the gradient of a velocity-time graph Acceleration = gradient y −y = x2−x 1 2 1 200−0 = 50−0 = 4 m/s​2 1.8 determine the distance travelled from the area between a velocity-time graph and the time axis. Distance can be determined by finding the area under a velocity-time graph as shown below: # Distance travelled = area under the graph = ½ (a+b)h = ½ (100 + 40) x 150 = ½ x 140 x 150 = 10500m #  y 2 −y 1 i) Acceleration in first 60s = x2 −x1 40−0 = 60−0 2 = 3 m/s​2 ii) Distance in 100s = ½ x b x h + l x b = ½ x 60 x 40 + 40 x 60 = 1200 + 2400 = 3600 m iii) Average Speed = dt = 2800/100 = 28 m/s # Maximum speed = 60 m/s Acceleration = y 2 −y 1 Part – 1 = x2 −x1 60 = 20 = 3 m/s y 2 −y 1 Part – 2 = x2 −x1 40−0 = 60−40 = 2 m/s y 2 −y 1 Part – 3 = x2 −x1 40−0 = 90−80 = 4 m/s​2 c) Forces, movement, shape and momentum 1.9 describe the effects of forces between bodies such as changes in speed, shape or direction Force is that which can change the state of rest or uniform motion of an object. It is simply pushes and pulls of one thing on another. If a body is thrown up in the air, what is the effect of gravity on the body? At first gravity reduces the speed of upward movement of the body and at a certain height it stops. So Force effects the speed. Take a sponge and squeeze it will change its shape. Throw a ball at a person in one direction. That person will hit the ball again i.e. apply force to the ball and it will change its direction. To sum up the examples, the effects that occur when a force is applied to an object are: 1. The object may start to move or stop moving. 2. The object may speed up or slow down. 3. The object may change its shape 4. The object may change its direction of movement. 1.10 identify different types of force such as gravitational or electrostatic Different sorts of Force: 1) Gravitational force or weight: The pull of earth due to gravity. 2) Normal Reaction: Simple reaction that stops something when to apply force to it. E.g.: A book is kept on the table which has a normal reaction on it. Otherwise the book would fall down. 3) Air Resistance: The resistivity or drag in the air while an object moves is called Air Resistance.E.g.: When a parachutist open the parachute the movement slows down for the opposite force acting in it. 4) Upthrust: Upthrust force acts only on liquid or air. It pushes an object upwards inspite of gravity. E.g.: A helium balloon moves upwards due to up thrust force. 5) Magnetic: Magnetic force is the attraction force between the poles of magnets. N=S 6) Electrostatic: Electrostatic force is the attraction force between charges. +=- 7) Tension: The pull at both ends of a stretched spring ,string, or rope. 8) Frictional force: the force produced when two objects slide one over another is called frictional force. 1.11 distinguish between vector and scalar quantities Scalar quantities are physical quantities that have magnitude only. Vector quantities however are physical quantities that possess both magnitude as well as direction. Scalar Vector Mass Displacement Time Velocity Distance Acceleration  Speed Force Volume Density Work Energy Power Difference: Scalar Vector Needs only size to express them Needs both size and direction to express them. Changes by changing size. Changes by changing size or direction or even both. Product of two scalar is a scalar i.e ​scalar Products of two vectors can be either be X​ scalar = scalar. scalar or vector i.e. vector X vector = scalar/vector. 1.12 understand that force is a vector quantity Force is a vector quantity due to the following reasons - It has magnitude i.e has the value of its size. It has direction. When applied force, an object moves with particular motion in a fixed direction. E.g: Gravitational force has one direction which is downwards. Upthrust has the direction of upwards. 1.13 find the resultant force of forces that act along a line Forces which act along a straight line can be added if the forces are in the same direction or subtracted if the forces are in the opposite direction. The force that you get after adding or subtracting is called the resultant force. The resultant force is a single force that has the same effect as all the other forces combined. Figure 1 Figure 2 Figure 1 shows that two forces: 150N and 50N are acting on an object A in the same direction and the object is moving. Figure 2 shows that a single from 200N is acting on the same object and the object moves at the same motion. So 200N is the resultant force of 150N and 50N. Examples are - i. Resultant force = (500 - 200)N = 300 N (towards right) ii. Resultant force = 1000 – 1000 = 0 N (rest object) 1.14 understand that friction is a force that opposes motion Friction is the force that causes moving objects to slow down and finally stop. The kinetic energy of the moving object is converted to heat as work is done by the friction force. Friction occurs when solid objects rub against other solid object and also when objects move through fluids(liquids and gases). Types of frictions: Kinetic friction: The friction that occurs when the object is in motion is called kinetic friction. E.g: Friction deduced in a moving car. Static friction: The friction produced when force is applied but the object doesn’t move is called static friction. E.g: a block is pulled but it doesn’t move because the force is not enough to move it. The friction produced in the block in this situation is the static friction. Rolling friction: When an object rolls around another object, a friction is produced. This is called rolling friction. E.g.: The car wheel moves around the axel and rolling friction is produced.  Fluid friction: The friction produced when two liquid layer side by side moves at different speed is called fluid friction. Solid-fluid friction: When a solid moves through a fluid, a friction is produced to the motion. This is called solid-fluid friction. Causes of friction: Ridges and bumps between the surfaces. The attraction force between the molecules of containing surfaces. Ways to reduce friction: By making the surface smooth, By using lubricating oil such as mobile, grease etc. Advantages of friction: We can walk and run due to friction. We can fix a nail in the wall due to friction. We can hold a pen due to friction. Disadvantages of friction: Friction causes wear and tear in the surface. It reduces the efficiency of the machines. There is wastage of energy due to friction. Experiment​: To investigate friction As shown on the diagram above, a block is set on the surface of the track. A nylon line is connected to it which passes over a pulley to a weight. There is friction between the surface of the block and the surface of the track. When the pull of weight equals to the friction then the block starts moving. So the amount of the weight that starts the block to move is equal to the friction. We can increase the friction by putting some masses over the and we will see that the more is the mass the more is the friction. We can make the track surface rougher such as byusing sand paper we will see the friction increases. 1.15know and use the relationship between unbalanced force, mass and acceleration: Balanced force - ​When two or more forces acting on an object cancels each other and there is no resultant force, then the forces are called balanced force. 200N and 300N are acting towards left on the object A. 500N force is acting on it towards right. The forces cancel each other. So there is no resultant force. So these forces are called balanced forces. Unbalanced force - ​When two or more forces acting on an object do not cancel each other fully and there is a resultant force, then the forces are called unbalanced force. 400N and 200N are acting on the object A towards right direction. 300N is acting towards left direction. The forces do not cancel each other fully. There is resultant force of 300N towards right. So their forces are unbalanced. Force= mass x acceleration In equation, F=ma (where, m=mass and a=acceleration) Fαa Force is directly proportional to acceleration. If force increases acceleration increases. Experiment​: To investigate F α a Working principle​ - ​The rate of change of momentum is directly proportional to the applied force and takes place in the direction of force. Apparatus required - Trolley Nylon line Pulley Ramp Bench top Mass hanger Diagram - Working procedure​ -​The force acting on the trolley is produced by the masses on the end of the nylon line. As the mass is increased, the trolley accelerates as well, so the force is increased by the transferring one of the masses from the trolley to the mass hanger. In the diagram-b, this increases the pulley force on the trolley, while keeping the total mass of the system the same. The acceleration of the trolley can be measured by taking a series of pictures at equal intervals of time using a digital video camera. Observation​ -​Here, using the digital video camera, as sequences of pictures are taken, the distance travelled from the start for each image is measured, since the time between each image is known, a graph of displacement against time can be drawn. The gradient of the displacement-time graph gives the velocity at a particular instant, so using the value data for a velocity-time graph can be obtained. The gradient of the velocity-time graph produced is the acceleration of the trolley. Graph - Conclusion​ -​The force and acceleration is same and this produces a straight-line graph which determines that force is directly proportional to force. So doubling the force acting on an object doubles its acceleration. Experiment​: To investigate a α 1/m The same experiment as above, only the force is kept constant and the mass of the trolley is varied. The graph shows the acceleration of the trolley plotted against 1/m. This is also a straight line passing through the origin, showing that acceleration is inversely proportional to mass. aα 1/m This means that for a given unbalanced force acting on a body, doubling the mass of the body will halve the acceleration. Combining Experiment 1 and 2, we get:  F = m xa One newton is the force needed to make a mass of one kilogram accelerate at one metre per second squared. 1.16 know and use the relationship between weight, mass and g: Weight is the pull of earth. To calculate it, use the formula: Weight = mass x gravitational acceleration W =mg Gravitational field strength: The pull of planet on an object of 1 kilogram is called gravitational field strength. It is also denoted by g, where in earth g= 10 m/s​2​ if there is no opposite force. Experiment​:To verify acceleration due to gravity using video camera We could measure the distance between two images of the tennis ball – say, the second and the third. This is the distance that the ball travelled during the second interval of one tenth of a second. The average velocity during this time is found by diving the distance travelled, 14.7 cm, by the time taken, 0.1s. This gives an average velocity of 147 cm/s or 1.47 m/s over the interval. If we repeat the calculation for the next tenth of a second, between 3 and 4m we find the average velocity has increased to 2.45 m/s. We can then use the equation for acceleration. The result of this experiment gives us a value for acceleration caused by the force of gravity. Experiment: To measure acceleration due to gravity using electromagnet Apparatus: ​Millisecond timer, metal ball, trapdoor and electromagnet. Procedure: 1. Set up the apparatus as shown. The millisecond timer starts when the ball is released and stops when the ball hits the trapdoor. 2. Measure the distance, s using a meter stick. 3. Flick the switch to release the ball and record the time, t from the millisecond timer. 4. Repeat for different values of s. 5. Calculate the values of g using the equation s = (g/2) t​2​. Obtain an average value for g. 6. Draw a graph of s against t​2​ and use the slope to find the value for g. Precautions/ Source of error: 1. For each height s repeat three times and take the smallest time as the correct value for t. 2. Place a piece of paper between the ball bearing and the electromagnet to ensure a quick release. 3. Remember to convert from milliseconds to seconds. 1.17 describe the forces acting on falling objects and explain why falling objects reach a terminal velocity Terminal velocity is the steady velocity of a falling object whose drag is balanced by the weight. How does a falling object reach terminal velocity? In a free falling object two types of force acts: Drag and Weight. The size of the drag force acting on an object depends on its shape and its speed. If the drag force of an object increases to a point which is equal to Weight, then the acceleration stops. It falls in a constant velocity known as terminal velocity. Reaching terminal velocity on a parachute: When a skydiver jumps from a plane at high altitude he will accelerate for a time and eventually reach terminal velocity. When she will open her parachute, this will cause a sudden increase in the drag force. At that time drag force will be higher than the weight and he will decelerate for some time. Later those forces will become equal and reach a new terminal velocity. 1.18 describe experiments to investigate the forces acting on falling objects, such as sycamore seeds or parachutes Sycamore seeds: We can measure the weight of the sycamore seeds using an electric balance. Now the sycamore seed is released from a high point. We will use a digital video camera to take the snaps of the moving seed. The video camera can take 25 snaps in one second. We can measure the acceleration of the ball at any point using the snaps of the moving seed. Now multiplying the mass of the seed by acceleration at any point we can find the unbalanced force acting on it. If we subtract the unbalanced weight from its weight, we will get the air resistance acting on the seed. Parachutes: When a parachute is released only the weight acts on it. We can use a force meter to determine the weight. When the parachute falls downward, air resistance acts on it in the upward direction. So the downward unbalanced force decreases. The force meter attached to the parachute gives a lower reading. As the parachute goes down the speed increases. The drag force also increases. The reading on the force meter decreases as well. A moment comes when the drag force becomes equal to the weight. In this situation the reading in the force meter becomes zero. If we want to find the air resistance at any momentum we will have to subtract the weight from the unbalanced force. This is how we can investigate the forces acting on a falling object. 1.19 describe the factors affecting vehicle stopping distance including speed, mass, road condition and reaction time Stopping distance: The stopping distance is the sum of Thinking distance and Braking distance. Thinking distance: The distance travelled after seeing an obstacle and till reaction. Braking distance​– ​The distance travelled after the brakes are applied. The thinking distance depends on the following factors - i. Whether the driver is tired or has taken alcohol or drugs. ii. On the visibility power of the driver. iii. On the speed of the car. The braking distance depends on the following factors -  i. Speed of the car:​ The more the speed is, the more the braking distance ​ ​V2​.​ will be; ​S α ii. Mass of the car​: As acceleration is equal to F/m, for constant braking force, the more is the mass, the less is the deceleration, the more is the braking distance. iii. Road condition:​ If the road is rough, the braking distance will be less. iv. Tyre condition:​ If the tyre is new (rough), there will be less braking distance. v. Braking system:​ For loose braking system, the braking distance will be more. 1.20 know and use the relationship between momentum, mass and velocity: Momentum is a quantity possessed by masses in motion (product of mass and velocity). Momentum is measure of how difficult it is to stop something that is moving. We calculate the momentum of a moving object using the formula: Momentum,p(kg m/s) = mass, m(in kg) x velocity, v (in m/s) P=mxv 1.21 use the idea of momentum to explain safety features Objects in a car have mass, speed and direction. If the object, such as a person, is not secured in the car they will continue moving in the same direction (forward) with the same speed (the speed the car was going) when the car abruptly stops until a force acts on them. Every object has momentum. Momentum is the product of a passenger's mass and velocity (speed with a direction). In order to stop the passenger's momentum they have to be acted on by a force. In some situations the passenger hits into the dashboard or windshield which acts as a force stopping them but injuring them at the same time.  1 Crumple Zone Cars are now designed with various safety features that increase the time over which the car’s momentum changes in an accident. Crumple zones are one of the safety features now used in modern cars to protect the passengers in an accident. The car has a rigid passenger cell with crumple zones in front and behind. During a collision, it increases the time during which the car is decelerating. This also reduce the force impacting on the passenger increasing their chances of survival. 2 Air Bags Many cars are now fitted with air bags to reduce the forces acting on passengers. The purpose of an airbag is to help the passenger in the car reduce their speed in collision without getting injured. An airbag provides a force over time. This is known as impulse. The more time the force has to act on the passenger to slow them down, the less damage caused to the passenger. 1.22 use the conservation of momentum to calculate the mass, velocity or momentum of objects If a moving object hits another slow or stationary object, it will result an equal force to both of the objects (according to Newton’s Third Law). That forces act in opposite directions and obviously for the same amount of time. This means the F x t for each is the same size. The moving object lost its momentum while the stationary object gained its momentum. So it is balanced. The total moment of the two objects is unchanged before and after the collision- ​momentum is conserved​. Momentum before the collision = momentum after the collision m​1u ​ ​ + m​2u ​ 1 ​ ​ = m1​ ​v​1​ + m2​ ​v​2​. ​ 2 Elastic and inelastic collisions In a collision, if the kinetic energy remains conserved, the collision is called elastic collision. Example- Collision between two gas molecules. In a collision if the kinetic energy does not remain conserved, the collision is called inelastic collision. Example - Collision between a truck and a micro-bus. Application of momentum principle:Explosion Two gliders are tied by a thread while the two ends contain two like poles of a magnet. The gliders are on the air track. Using a match stick we can burn the thread. When the thread is cut, the two gliders move away in opposite direction. If the masses of the two gliders are same, the speed of the gliders will also be equal. It means that the momentum of the two gliders is equal and opposite. That is the total momentum difference is zero which was the same before the collision. It verifies the law of conservation of momentum. Before collision After collision Both rest Both can stop Both moving Both moving (same/ opposite) One moving Both can be one object Law of conservation of momentum is only verified if two forces act on it-- action & reaction. Application of momentum principle: Rockets Rocket motors use the principle of conservation of momentum to propel spacecraft through space. They produce a continuous, controlled explosion that forces large amount of fast-moving gases (produced by fuel burning) out of the back of the rocket. The spacecraft gains an equal amount of momentum in the opposite direction to that of the moving exhaust gases and moves upward with a very high speed. 1.23 use the relationship between force, change in momentum and time taken: Initial momentum of object = mu Final momentum = mv Therefore increase in momentum = mv-mu Rate of increase of = (mv-mu)/t momentum = m(v-u)/t = ma = Force Force = Rate of increase of momentum Force = Change in momentum / time 1.24 demonstrate an understanding of Newton’s third law Newton’s thirds law: “For every action there is an equal and opposite reaction.” Newton’s third law states four characteristics of forces: Forces always occur in pairs (action and reaction force.) The action and reaction are equal in magnitude. Action and reaction act opposite to one another. Action and reaction act on different bodies. Action and reaction do not cancel each other 1.25 know and use the relationship between the moment of a force and its distance from the pivot: moment = force × perpendicular distance from the pivot moment =F x d The turning effect of a force about a hinge or pivot is called its moment. In other words, it is the product of force and the perpendicular distance from the pivot to the line of action of the force. It is measured in Newton meter (Nm). There are two types of moment: (i) Clockwise moment & (ii) Anti-clockwise moment When a force causes an object to turn in a clockwise direction, it is called a Clockwise Moment. When a force causes an object to turn in an anti-clockwise direction, it is called a Anti-clockwise moment. 1.26 recall that the weight of a body acts through its centre of gravity Mass is the amount of matter an object has. Every part of an object forms part of its overall mass. But when we try to balance an object on a point, there will only be one place where it will balance. You can therefore think of the mass of an object being concentrated at this point, known as the centre of mass or gravity. If we support the centre of gravity of the object, the object won’t fall no matter how wide it is. Because the moment of the all sides are balanced and there will be no clockwise or anti-clockwise movement. Stability of centre of gravity A stable object is one that is difficult to push over; when pushed and then released it will tend to return to its original position. Stability can be increased by: i. By increasing the base area.  ii. By decreasing the height of COG. Experiment​: To determine the position of the centre of gravity of an uniform object using balancing method Balance the object keeping over a scale and draw the line of contact. Balance the object on another axis keeping it over the same scale and draw the line of contact again. The two lines intersect at a point. This point gives the COG. Experiment​: To determine the position of the centre of gravity of a plane lamina with irregular shape of non-uniform thickness or density Apparatus: ​Retord stand, plumbline, cork and pin Procedure: 1. Make three small holes near the edge of the lamina. The holes should be as far apart as possible from one another.  2. Suspend the lamina through one of the holes using a pin. 3. Hang a plumbline on the pin in front of the lamina. 4. When the plumbline is steady, draw a line on the lamina over the plumbline. 5. Repeat the above for other two holes. 6. The point of intersection of the three lines is the position of the centre of gravity. Precautions​: 1. The holes must be small so that not too much of the lamina is removed. 2. The lamina should be free to swing above its point of suspension. 1.27 know and use the principle of moments for a simple system of parallel forces acting in one plane Solving Problems related to Principle of Moments Example - 1 Step 1: Identify what are forces that will give rise to clockwise / anti-clockwise moment Step 2: Find the clockwise / anticlockwise moment Step 3:  Equate the clockwise and anticlockwise moments Example – 2 F​2 d​ ​ 2​ + F​1 d​ ​ 1= ​ F​3 d​ ​ 3+ ​ F​4 d​ ​ 4 10 x 20 + 20 x 10 = 5 x 20 + 15 x d​4 400 – 100 = 15 x d​4 d​4 = ​ 300/15 d​4 = ​ 20m Example – 3 At position A, the object is of 400N at a distance 1.5m from the pivot. What should be the distance of object B from the pivot is of 500N and the see-saw is at equilibrium position. At equilibrium, sum of clockwise moment = sum of anti-clockwise moment F​1 d​ ​ 1​ = F​2 d​ ​ 2 400 x1.5 = 500 x d​2 d​2 = ​ 600/500 d​2 = ​ 1.2 m Example – 4 In a crane, the force arm d​1​ = 2m and weight of 5000N is put at the force arm. What maximum load the crane can raise in the load arm d​2​ is 10m? Sum of CWM = Sum of ACWM W x d​1​ = F x d​2 W ×d F= d2 5000×2 F= 10 F = 1000N Experiment​:To verify the principle of moment A uniform beam AD is put at point P on a support. The beam is balanced. Now, we will put four different beam at different distances in a way so that the beam restores the balance again. Now, calculate the moment for the weights Moment for W​1​ = W​1​d​1 Moment for W​2​ = W​2​d​2 Moment for W​3​ = W​3​d​3 Moment for W​4​ = W​4​d​4 Now, sum of clockwise moments = W​3​d​3 + ​ W​4​d​4 Sum of anti-clockwise moments = W​1​d​1 + ​ W​2​d​2 Now, if we put the values of constants, we will see that W​1​d​1 ​+ W​2​d​2​ = W​3​d​3 ​+ W​4​d​4 i.e. Sum of anti-clockwise moment = sum of clockwise moment So the principle of moment is verified. 1.28 understand that the upward forces on a light beam, supported at its ends, vary with the position of a heavy object placed on the beam a) An object weighing 400 N is placed in the middle of the beam. The beam is not moving,so the upward and downward forces must be balanced. b) As the object is placed in the middle of the beam, the upward forces on the ends of the beam are same as each other. If it is moved right to one end of the beam, then the upward force will all be at that end of the beam. As it is moved along the beam, the upward forces at the ends of the beam change. In c) he is ¼ away from the plant. The upward force on the support nearest to him is ¾ of his weight and the upward force on the end of furthest beam is only ¼ of his weight. x + y = 400x× ¼ = y × ¾ x × ¼ = (400 − x) × ¾x = 3(400 − x)x = 1200 – 3x4x = 1200x = 300 y = 400 – x = 400 – 300 = 100 1.29 describe experiments to investigate how extension varies with applied force for helical springs, metal wires and rubber bands Experiment​: Investigating extension with applied force in spring Apparatus: Spring/Wire/Rubber-band Scale Some masses Clamp and stand Mass hanger Working procedure: i) Take the length of the normal condition. ii) Add a mass in the mass hanger and determine the extension by using the porter and the scale. iii) Add another mass gradually and determine the extension in all cases. iv) Plot a graph of extension and relevant loads. Observation with helical spring: Since the graph of load & extension is a straight line, which proves the extension and load are directly proportional. Observation with rubberband: Since the graph didn’t produce a straight line, extension is not directly proportional to load force. But extension still increases as the force is applied. Observation with metal wire: 1.30 understand that the initial linear region of a force-extension graph is associated with Hooke’s law Hooke’s law, “Within the elastic limit, extension is directly proportional to the load i.e. e α f” Hooke measured the increase in length (extension) produced by different load forces on springs. The graph he obtained by plotting force against extension looked like that below. This straight line passing through the origin shows that the extension of the spring is proportional to the force. The relationship is known as ​Hooke’s law. Hooke’s Law only applies if you do not stretch a spring to far. At a point the elastic limit it starts to stretch more for each successive increase in the load force. Once you have stretch a spring beyond this limit it has changed shape permanently and will not return to its original shape. 1.31 describe elastic behaviour as the ability of a material to recover its original shape after the forces causing deformation have been removed. Objects showing elastic behaviour has the ability to return to its original shape after the forces causing its shape are removed. This property is called elasticity. Examples of objects showing elastic behaviour are coiled springs. Uses of spring: 1. use to absorb bumps in the road or suspension spring in the car or cycle. 2. In beds and furnitures they used to make sleeping and sitting more comfortable. 3. used in door locks to hold bolts and catches closed and to make doors close automatically. 4. used in measuring devices like spring balance or bathroom scales. The materials which do not exhibit elasticity i.e. they do not return to its original position after stretching force is removed are called plastic materials. Examples are putty, plasticine. Section 2: Electricity a) Units 2.1 use the following units: ampere (A), coulomb (C), joule (J), ohm (), second (s), volt (V), watt (W). Unit of current: ampere (A) Unit of charge: coulomb (C) Unit of energy: Joule (J) Unit of resistance: ohm​ (Ω) Unit of time: second (s) Unit of voltage or potential difference: volt (V) Unit of Power: watt (W) b) Mains electricity 2.2 understand and identify the hazards of electricity including frayed cables, long cables, damaged plugs, water around sockets, and pushing metal objects into sockets Mains electricity​: The source of electricity in our houses is called mains electricity. Electricity meter​: The meter that measures the electrical energy we consume in our house is called electricity meter. Fuse box(or Consumer unit):​ The box that contains all fuse and circuit breakers in a circuit is called fuse box. Ring main circuit​: Wires that leave the fuse box are hidden in the walls or floors around each room. These wires are connected to form ring main circuits. Individual equipments are connected to these circuits using plugs. It consists of three wires: live wire, neutral wire and earth wire. Live wire​: The wire that contains the electricity all the time is called live wire. Neutral wire​: The wire that usually doesn’t contain the electricity but when it is connected with the live wire then it also become live. The neutral wire completes the circuit. Earth wire​: The earth wire usually has no current flowing through it. It is there to protect user if an appliance develops a fault. Electricity is very useful, but it can be dangerous if it is not used safely. The following hazards that increase the chances of severe and possibly fatal electric shocks are: frayed cables, any damaged insulation can expose ‘live’ wires. Long cables, as they are more likely to get damaged or trip people up. Damage to plugs or any insulating casing on any mains operated devices. Water around electric sockets or mains operated devices. Pushing metal objects into the mains sockets – usually only a problem with very young children, solved by using socket covers. 2.3 understand the uses of insulation, double insulation, earthing, fuses and circuit breakers in a range of domestic appliances Insulation: Some appliances are cased with insulators like plastic rather than metal to prevent user from receiving shock. This casing is called insulation. Double Insulation:Some appliances are double insulated; as well as all their wiring being insulated the outer casing of the appliances is also made of an insulating material. This means there is no chance of an electric shock from the casing – double insulation is often used with electric kettles and power tools like electric drills. Earthing: Many appliances have a metal casing. This should be connected to earth wire so that if the live wire becomes frayed or breaks and comes into contact with the casing, the current will pass through the earth wire rather than the user. The current in the earth wire is always large enough to blow the fuse and turning off the circuit. So the user is safe from electric shock. Fuses: Fuse is a safety device usually in the form of a cylinder or cartridge which contains a thing piece of wire made from a metal that has low melting point. If too large a current flows in the circuit the fuse wire becomes very hot and blows, shutting the circuit off. This prevents you getting a shock and reduces the possibility of an electrical fire. One the fault in the current is corrected, it should be replaced again. Circuit Breakers or Trip switches: Circuit Breaker is similar to fuses. If too large a current flows in a current a switch opens making the circuit incomplete. Once the fault in the circuit is corrected, the switch is reset, usually by pressing a reset button. inside outside How does a circuit breaker work? When high current flows, the electromagnet in it gains its magnetism and attract the iron catch towards it. This separated the contact and the circuit discloses. Switches​: Switches in main circuit should always be included in the live wire so that when the switch is open, no electrical energy can reach an appliance. If the switch is included in the neutral wire, electrical energy can still enter an appliance, and could possibly cause an electric shock. 2.4 understand that a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts Normal wiring in the house are said to have low resistance and the current pass through them easily. Heating elements like nichrome wire have high resistance. When current flows through them current cannot pass, and the energy is transferred to heat energy and the element heats up.It is also used in the lights – normal light bulbs have a very thin filament which gets so hot when current passes through it that it glows white. We use the heating effect of current in electric kettle, iron, filament lamps, fan heaters, hair dryers etc. 2.5 know and use the relationship: power = current × voltage P=I×V and apply the relationship to the selection of appropriate fuses Power is amount that represents how much voltage or energy is converted every second. It is calculated using this equation: Power, P (in watts) = current, I (in amps) x voltage, V (in volts) P= I x V Fuses in plugs are made in standard ratings. The most common are 3A, 5A and 13A. The fuse should be rated at a slightly higher current than the device needs: if the device works at 3A, use a 5A fuse if the device works at 10A, use a 13A fuse 2.6 use the relationship between energy transferred, current, voltage and time: energy transferred = current × voltage × time E=I×V×t The power of an appliance (P) tells you how much energy it converts each second. This means that the total energy (E) converted by an appliances is equal to its power multiplied by the length of time the appliance is being used. Total energy, E(in joules) = power, P (in watts) x time, t (in seconds) E= P x t Since, P = I x V E= I x V x t 2.7 understand the difference between mains electricity being alternating current (a.c.) and direct current (d.c.) being supplied by a cell or battery. Alternating current: If the current constantly changes direction, it is called alternating current, or a.c.. Mains electricity is an a.c. supply, with the UK mains supply being about 230V. It has a frequency of 50Hz (50 hertz), which means it changes direction, and back again, 50 times a second. The diagram shows an oscilloscope screen displaying the signal from an a.c. supply. Alternating current is useful in electricity generator and transformers. Direct current: If the current flows in only one direction it is called direct current, or d.c. Batteries and cells supply d.c. electricity, with a typical battery supplying maybe 1.5V. The diagram shows an oscilloscope screen displaying the signal from a d.c. supply. Alternating current can be converted to direct current by using a rectifier. This direct current is made uniform by filter circuit. c) Energy and potential difference in circuits 2.8 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting Series Circuit: one switch can turn off the components on and off together if one bulb ( or other component) breaks, it causes a gap in the circuit and all of the other bulbs will go off the voltage supplied by the cell or mains supply is “shared” between all the components, so the more bulbs you add to a series circuit the dimmer they all become. The larger the resistance of the component, the bigger its “share of voltage” Parallel Circuit: switches can be placed in different parts of the circuit to switch each bulb on and off individually or all together if one bulb (or other components) breaks, only the bulbs on the same branch of the circuit will be affected each branch of the circuit receives the same voltage, so if more bulbs are added to a circuit in the parallel they all stay bright. Decorative lights are usually wired in series. Each bulb only needs a low voltage, so even when the voltage from the mains supply is shared between them, each bulb still gets enough energy to produce light. If one of the bulbs is not in its holder properly, the circuit is not complete and none of the bulbs will be on. In the past, if the filament in one of the bulbs broke, all of the other bulbs would go out. Today, many bulbs used in decorative lights are provided with a ‘shunt’ which allows current to continue to flow through the bulb even after the filament has broken. The lights in our house are wired in parallel. Each bulb can be switched on and off separately and the brightness of the bulbs does not change. If one bulb breaks or is removed, you can still use the other lights. 2.9 understand that the current in a series circuit depends on the applied voltage and the number and nature of other components Series circuit​: In a series circuit the current is the same in all parts. Current is not used up as it passes around a circuit. The size of the current is a series circuit depends on the voltage supplied to it, and the number and nature of the other components in the circuit. In a circuit if more cell is attached, the current will increase as more energy is being given to the electrons. If more resistance is attached to the circuit the current will get less. But current is same at all points in a series circuit. Parallel circuit​: In parallel circuit, current varies with the resistance and voltage. Voltage are same at all branches. This circuit shows a 10​Ω and 20 Ω resistor connected in parallel to a 6V cell of negligible internal resistance. The p.d. across 10 Ω and 20Ω resistors is 6V. I​1​ = 0.6A I​2 = ​ 0.3 A As the resistance in I​2​ is higher, the current is small. I​3​ = I​1​ + I​2 The ​ current in a parallel circuit is shared between the branches depending on the resistance. 2.10 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentally a) Resistors and wires obey Ohm’s law. Current, I, is proportional to voltage, v, and the graphs are straight lines which pass through the origin (0,0) of the scales. b) The filament in a lamp is a metal wire but it gets very hot indeed. The resistance of a metal increases with temperature – the graph curves when the lamp reaches its working current and temperature. c) Diodes have a very large resistance when voltage is applied in the ‘wrong’ direction – this is shown by the horizontal line when the voltage is negative. When the voltage is in the ‘right’ direction (forward biased), when it reaches around 0.7v, the resistance drops to a small value – the graph curves and become very steep. Experiment​: To investigate how current varies with voltage. (Ohm’s law) The resistance of a component is related to the current through it and the voltage across it by the equation V = I x R. If we wish to find the resistance of a component, this equation can be rearranged to give R = V/I. The circuit in Figure can be used to investigate this relationship for a piece of resistance wire. When switch S is closed for the readings on the ammeter and voltmeter are noted. The value of the variable resistor is then altered and a new pair of readings taken from the meters. The whole process is repeated at least six times, the results are placed into a table and a graph of current against voltage is drawn. Current, I (A) Voltage, V (v) 0.0 0.0 0.1 0.4 0.2 0.8 0.3 1.2 0.4 1.6 0.5 2.0 The graph in Figure is a straight line passing through the origin. This tells us that the current flowing through the wire is directly proportional to the voltage applied across its end – that is, if the voltage across the wire is doubled the current flowing through it doubles. 2.11 describe the qualitative effect of changing resistance on the current in a circuit R α 1/I Resistance is inversely proportional to current. Higher resistance means lower current and higher current means lower resistance. In other words resistance is the opposition of current. Resistance blocks charge flow. 2.12 describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature Light Dependant Resistors: ​An LDR is a light dependant resistor. Its resistance changes with the intensity of light. In dark condition LDRs contain few free electrons and so have a high resistance. If however light is shone onto an LDR more electrons are freed and the resistance decreases. LDRs are often used in light sensitive circuits in devices such as photographic equipment, automatic lightning controls and burglar alarms. Thermistor: ​A thermistor is a temperature dependant resistor. It is made from a semiconducting material such as silicon or germanium. At room temperature the number of free electrons is small and so the resistance of a thermistor is large. If however if it is warmed the number of the electrons increases and its resistance decreases. Thermistors are often used in temperature-sensitive circuits in devices such as fire alarms and thermostats. 2.13 know that lamps and LEDs can be used to indicate the presence of a current in a circuit A light-emitting diode (LED) is a special kind of diode that glows when electricity passes through it. Most LEDs are made from a semi-conducting material called gallium arsenide phosphide. LEDs can be bought in a range of colours. They can also be bought in forms that will switch between two colours (bi-colour), three colours (tri-colour) or emit infra-red light. In common with all diodes, the LED will only allow current to pass in one direction. The cathode is normally indicated by a flat side on the casing and the anode is normally indicated by a slightly longer leg. The current required to power an LED is usually around 20 mA. 2.14 know and use the relationship between voltage, current and resistance: voltage = current × resistance V=I×R 2.15 understand that current is the rate of flow of charge The size of an electric current indicates the rate at which charge flows. Charge(Q) is measured in coulombs (C). Current is measured in amperes (A). If 1 C of charge flows along a wire every second the current passing the wire is 1A. 2.16 know and use the relationship between charge, current and time: charge = current × time Q=I×t 2.17 know that electric current in solid metallic conductors is a flow of negatively charged electrons Current is the flow of charge. One coulomb of charge is equivalent of the charge carried by approximately six million, million, million (6 x 10​18​) negative electrons. Charge direction when connected to a battery In conductors some electrons are free to drift. But the number of electrons flowing in any one direction is roughly equal to the number flowing in the opposite direction. There is therefore no overall flow of charge. However, if a cell or battery is connected across the conductor, more of the electrons now flow in the direction away from the negative terminal and towards the positive terminal, than in the opposite direction. There is now a net flow of charge. Electrons/charges move from the negative terminal to positive. But when you are dealing with topics such as circuit and motors, it is still considered that current flow from positive to negative. This is called conventional current. 2.18 understand that: voltage is the energy transferred per unit charge passed the volt is a joule per coulomb. As the charges flow around a circuit, the energy they carry is converted into other forms of energy by the components they pass through. The voltage across each component tells us how much energy it is converting. If the voltage across a component is 1v, this means that the component is changing 1J of electrical energy into a different kind of energy each time 1C of charge passes through it. d) Electric charge 2.19 identify common materials which are electrical conductors or insulators, including metals and plastics Conductors: Electrical conductors are materials that allow current to pass through them. Conductors have free electron diffusion to pass current. Metals like copper, silver, aluminium havefree electrons and can conduct electricity. Insulators: Insulators do not conduct electricity because they don’t have free electrons. Examples of insulators are plastics, rubber, wood etc. 2.20 describe experiments to investigate how insulating materials can be charged by friction Experiment​: To investigate how insulating materials can be charged by friction Apparatus: Glass rod, silk cloth, electroscope Procedure: 1. Take a glass rod and silk cloth. 2. Rub the rod with the cloth. 3. Now, take any of the two materials near the metal plate of an electroscope. Observation 1. You will notice that the leaf below will deflect. 2. This will prove that charge can be produced by friction. 2.21 explain that positive and negative electrostatic charges are produced on materials by the loss and gain of electrons If two materials are rubbed together electrons will be transferred. The one that gains electrons will be negatively charged and the one that losses electrons will be positively charged. Materials Positive charge Negative charge Glass rod rubbed with silk glass Silk Ebonite rod rubbed with fur fur ebonite Perspex ruler rubbed with Perspex Duster woolen Plastic comb rubbed with hair Plastic comb hair Polythene strip rubbed with duster Polythene woolen duster Cellulose acetate rubbed acetate duster with woolen duster 2.22 understand that there are forces of attraction between unlike charges and forces of repulsion between like charges Similar charges repel each other and unlike charges attract each other. The attraction and repulsion occurs because of electrostatic force. Experiment​: To investigate unlike charge attracts Apparatus: Two pieces of glass rods. One piece of silk cloth Insulating thread. Diagram: Procedure: 1. Two glass rods are rubbed by silk cloth. The rods become positively charged and the cloth becomes negatively charged. 2. One positive charged glass rod is hung by an insulating thread. 3. Another positively charged glass rod is approached towards the hung rod. Observation: We will see that the hung rod move away. Conclusion: Like charges repels. Experiment​: To investigate that like charge repels. Apparatus: One piece of glass rod One piece of ebonite rod Two pieces of silk rod Insulating thread. Diagram: Procedure: 1. Two silk clothes are taken. When the glass rod is rubbed with the silk cloth, the glass rod becomes positively charged. Again, when with another silk cloth, the ebonite rod is rubbed, it becomes negatively charged. 2. The positively charged glass rod is hung by an insulating thread. 3. The negatively charged ebonite rod is approached towards the hung rod. Observation: We will see the hung rod moves towards the glass rod. Conclusion: Unlike charges attract. Experiment​: Showing that a charged object can attract an uncharged object If you charge a balloon by rubbing it against your jumper or your hair and then hold the balloon against a wall, you will find that the balloon sticks to the wall. There is an attraction between the charged balloon and the uncharged wall. After the balloon has been charged with static electricity, but before it is brought close to the wall, the charges will be distributed. The balloon is negatively charged and the wall is uncharged – that is, the equal numbers of positive and negative charges. As the negatively charged balloon is bought closer to the wall some of the negative electrons are repelled from the surface of the wall. This gives the surface of the wall a slight positive charge that attracts the negatively charged balloon. 2.23 explain electrostatic phenomena in terms of the movement of electrons An electrostatic phenomenon is an event where electricity has a special effect, for example a static shock. Electrons move from one material to another. Materials with a negative charge will look for some way to earth like clouds through lightning. 2.24 explain the potential dangers of electrostatic charges, eg when fuelling aircraft and tankers In some situations the presence of static electricity can be a disadvantage. As aircraft fly through the air, they can become charged with static electricity. As the charge on an aircraft increases so too does the potential difference between it and earth. With high potential differences her is the possibility of charges escaping to the earth as a spark during refueling, which could cause an explosion. The solution to this problem is to earth the plane with a conductor as soon as it lands and before refueling commences. Fuel tankers that transport fuel on roads must also be earthed before any fuels is transferred to prevent sparks causing a fire or explosion. Television screens and computer monitors become charged with static electricity as they are used. The charges attract light uncharged particles-that is dust.  Our clothing can, under certain circumstances become charged with static electricity. When we remove the clothes there is the possibility of receiving a small electric shock as the charges escape to the earth. Workers handing electronic components must take care not to become charged by static as this can easily destroy expensive components. They wear earthing straps and work on earthed metal benches to prevent this. 2.25 explain some uses of electrostatic charges, eg in photocopiers and inkjet printers. Electrostatic charges can be used in electrostatic paint spraying, inkjet printers, photocopiers, electrostatic precipitators etc. Electrostatic paint spraying Painting an awkwardly shaped object such as bicycle frame with a spray can be very time consuming and very wasteful of paint. Using Electrostatic spraying can be the process efficient. Let the metal spray nozzle be connected to a positive terminal so the paint that emerges will be positive charged. The bicycle frame should be connected to a wire and it will become negatively charged. The positively charged paint will be attracted to the frame. There is the added benefit that paint is attracted into places, such as tight corners that might otherwise not receive good coating. Inject Printers Many modern printers use inkjets to direct a fine jet of ink drops onto paper. Each spot of ink is given a charge so that as it falls between a pair of deflecting plates, electrostatic forces direct it to the correct position. The charges on the plates change hundreds of times each second so that each drop falls in a different position, forming pictures and words on the paper as required. Photocopiers In photocopiers, the paper is shone in bright light which reflects to a rotating drum. The dark writings and pictures do not reflect. As a result the light removes the charges in the drum. Carbon powder attaches to the charges in the drum and the pictures and writings are pasted into a sheet of paper. Electrostatic precipitators Many heavy industrial plants, such as steel-making furnaces and coal fired power stations, produce large quantities of smoke. This smoke carries small particles of ash and dust into the environment, causing health problems and damage to buildings. One way of removing these pollutants from the smoke is to use electrostatic precipitators. As the smoke initially rises up the chimney, it passes through a mesh of wires that are highly charged. As they pass through the mesh, the ash and dust particles become negatively charged. Higher up the chimney these charged particles are attracted by and stick to large metal earthed plates. The cleaner smoke is then released into the atmosphere. When the earthed plates are completely covered with dust and ash, they are given a sharp rap. The dust and ash fall into collection boxes, which are later emptied. Section 3: Waves a) Units 3.1 use the following units: degree (°), hertz (Hz), metre (m), metre/second (m/s), second (s). Unit of an angle: degree (​o​) Unit of frequency: hertz (Hz) Unit of distance or wavelength: metre (m) Unit of speed/velocity: metre/second (m/s) Unit of time-period: second (s) b) Properties of waves 3.2 understand the difference between longitudinal and transverse waves and describe experiments to show longitudinal and transverse waves in, for example, ropes, springs and water Waves can transfer energy and information from one place to another without transfer of matter. Waves can be divided into two types: mechanical waves and electromagnetic waves. Mechanical waves can be of two types: transverse and longitudinal. Transverse waves: ​A transverse wave is one that vibrates or oscillates, at right angles to the direction in which the energy or wave is moving. Example of transverse waves include light waves and waves travelling on the surface of water. Longitudinal waves: ​A longitudinal wave is one in which the vibrations or oscillations are along the direction in which the energy or wave is moving. Examples of longitudinal waves include sound waves. Transverse wave don’t need medium to move. Longitudinal wave needs medium to move. Experiment​: To show different types of waves in spring. Transverse – If you waggle on end of a slinky spring from side to side you will see waves travelling through it. The energy carried by these waves moves along the slinky from one end to the other, but if you look closely you can see that the coils of the slinky are vibrating across the direction in which the energy is moving. This is an example of transverse wave. Longitudinal – If you push and pull the end of a slinky in a direction parallel to its axis, you can see energy travelling along it. This time however the coil of the slinky are vibrating in direction that are along its length. This is an example of longitudinal wave. Experiment​: To create water waves using a ripple tank When the motor is turned on the wooden bar vibrates creating a series of ripples on the surface of water. A light placed above the tank creates pattern of the water waves on the floor. A light placed above the tank creates patterns of the water waves on the floor. By observing the patterns we can see how the water waves are behaving. 3.3 define amplitude, frequency, wavelength and period of a wave Amplitude: Amplitude is the maximum displacement of a part of the medium from its rest position. Wavelength: The distance between a particular point on a wave and the same point on the next wave (for example, from crest to crest) is called the wavelength (λ). Frequency: The number of waves produced each second by a source, or the number passing a particular point each second is called frequency(​ ​f​). Period: The period of a wave is the time for one complete cycle of the waveform. Experiment​: Adjusting ripple tank to investigate wavelength and frequency The motor can be adjusted to produce a small number of waves each second. The frequency of the waves is small and the pattern shows that the waves have a long wavelength. At higher frequencies, the water waves have shorter wavelengths. The speed of the waves does not change. Experiment​: Demonstrating refraction using ripple tank Refraction, the bending of light waves as they pass from one material to another, can be demonstrated by reducing the depth of water in the ripple tank (with a transparent glass or plastic sheet). Ripples travel more slowly if the depth of the water in the ripple tank is smaller. When setting up a ripple tank it is therefore important that the tank is level. Another problem with ripple tanks is unwanted reflection from the sides of the tank; these result in pretty patterns but make analysts of what you see very difficult. Most ripple tanks have sloping sides to reduce unwanted reflections. Experiment​: To demonstrate diffraction using vibrating bar To show the interesting effects of diffraction you need to set up continuous plane wavefronts and (circular wavefronts respectively). This is done with a vibrating bar placed wither directly in contact with the water or with two dippers just touched the water for circular wavefronts. The frequency of vibration is controlled frequency of the waves is controlled by varying the speed of electric motor attatched to the beam. 3.4 understand that waves transfer energy and information without transferring matter Waves are means of transferring energy and information from place to place. These transfers take place with no matter being transferred. Mobile phones, satellites etc. rely on waves. Example: If you drop a large stone into a pond, waves will be produced. The waves spread out from the point of impact, carrying to all parts of the pond. But the water in the pond does not move from the centre to the edges. 3.5 know and use the relationship between the speed, frequency and wavelength of a wave: wave speed = f requency × wavelength v = f× λ 3.6use the relationship between frequency and time period f requency, f (in hertz) = time period, T1 (in seconds) 1 f= T 3.7 use the above relationships in different contexts including sound waves and electromagnetic waves As all wave share properties the above relations can be used for any type of wave. P – 1​: The period of a wave is 0.01 second. What is its frequency? Ans​: Frequency = 1/T = 1/0.01s = 100 Hz P – 2​: The frequency of a wave is 250 Hz and the wavelength is 0.02m. What is speed of the wave? Ans​: v = f λ = 250 Hz x 0.02s = 5 m/s 3.8 understand that waves can be diffracted when they pass an edge Diffraction is the slight bending of waves as it passes around the edge of an object. The amount of bending depends on the relative size of the wavelength of light to the size of the opening. If the opening is much larger than the wave's wavelength, the bending will be almost unnoticeable. However, if the two are closer in size or equal, the amount of bending is considerable. 3.9 understand that waves can be diffracted through gaps, and that the extent of diffraction depends on the wavelength and the physical dimension of the gap. Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path. Water waves have the ability to travel around corners, around obstacles and through openings. This ability is most obvious for water waves with longer wavelengths. Diffraction can be demonstrated by placing small barriers and obstacles in a ripple tank and observing the path of the water waves as they encounter the obstacles. The waves are seen to pass around the barrier into the regions behind it; subsequently the water behind the barrier is disturbed. The amount of diffraction (the sharpness of the bending) increases with increasing wavelength and decreases with decreasing wavelength. In fact, when the wavelength of the waves is smaller than the obstacle, no noticeable diffraction occurs. c) The electromagnetic spectrum 3.10 understand that light is part of a continuous electromagnetic spectrum which includes radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations and that all these waves travel at the same speed in free space The electromagnetic spectrum is a continuous spectrum of waves which includes the visible spectrum. 1) they all transfer energy 2) they are all transverse waves 3) they all travel at speed of light in vacuum (3x10​8​ m/s) 4) they can all be reflected, refracted and diffracted 3.11 identify the order of the electromagnetic spectrum in terms of decreasing wavelength and increasing frequency, including the colours of the visible spectrum Different frequencies and wavelength differ them into different groups and consequently have different properties. Radio waves have the lowest frequency and the longest wavelength. Gamma rays have the highest frequency and the shortest wavelength. A mnemonic can help: ​R​un ​M​iles ​I​n ​V​ery ​U​npleasant e​X​treme ​G​ames. Colours of the visible spectrum There are seven colours in the visible spectrum: red, orange, yellow, green, blue, indigo and violet. Red has the longest wavelength and lowest frequency. A mnemonic can help: ​R​ichard ​O​f ​Y​ork ​G​ave ​B​attle ​I​n ​V​ain The EM spectrum is continuous – it is only broken upto into distinct zones for convenience. For example, the visible light spectrum is made up of an indeterminate number of colours that blend smoothly from on shade to the next. 3.12 explain some of the uses of electromagnetic radiations, including: Radio waves​: It is used in communicating information. This can be speech, radio and television, music and encoded messages like computer data, navigation signals and telephone conversations. The properties that make radio waves suitable for communicating are: Radio waves can travel quickly. Can code information. Can travel long distance through buildings and walls. It is not harmful. Microwaves​: Microwaves are used in microwave oven which cooks food more quickly than in normal oven. Microwaves are also used in communications. The waves pass easily through the Earth’s atmosphere and so are used to carry signals to orbiting satellites. From here, the signals are passed on to their destination. Messages sent to and from mobile phones and radarare also carried by microwaves. Infrared​: Special cameras designed to detect infra-red waves can be used to create image even in the absence of visible light. The image can be created because of the different temperatures of objects. Wavelength of infrared from warm objects is shorter than the infrared from cool objects. Infra-red radiation is also used in remote controls for televisions, videos and stereo systems. Moreover it is used in heating materials like heater. Visible light​: The main use of visible light is to see. Visible light from lasers is used to read compact discs and barcodes. It can also be sent along optical fibres, so it can be used for communication or for looking into inaccessible places such as inside of the human body. Furthermore, it has uses in photography too. Ultraviolet​: Some chemicals glow when exposed to UV light. This property of UV light is used in security markers. The special ink is invisible in normal lights but becomes visible in UV light. UV light is also used in fluorescent lamps, to kill bacteria, to harden fillings and disco ‘black’ lights. Some insects can see into the ultraviolet part of spectrum and use this to navigate and to identify food sources. X-rays​: X-ray is used to take pictures of patient’s bone to determine any fracture. X-rays are also used in industry to check the internal structures of objects-for example: to look for cracks and faults in buildings or machinery- and at airport as part of the security checking procedure.The X-rays produced by collapsing stars are also used in radio astronomy. Gamma rays​: They are used to sterillise medical instruments, to kill micro-organisms so that food will keep for longer and to treat cancer using radiotherapy. 3.13 understand the detrimental effects of excessive exposure of the human body to electromagnetic waves, including: and describe simple protective measures against the risks. Microwaves​: Micro waves might cause internal heating of body tissue. For this microwave ovens have metal screens that reflect microwaves and keep them inside the oven. It also has perceived risk of cancer. It can be prevented by closing oven doors and using hands-free cell phones. Infrared​: The human body can be harmed by too much exposure to infra-red radiation, which can cause skin burning and cell damage. It can be prevented by avoiding hot places, using reflective clothing and avoiding exposure to sun. Visible light: ​Visible light can cause eye damage. It can be prevented by sun glasses and avoiding exposure to the sun. Ultraviolet​: Overexposure of ultraviolet light will lead to sunburn and blistering. This can also cause skin cancer, blindness and damage to surface cells. Protective goggles or glasses and skin creams can block the UV rays and will reduce the harmful effects of this radiation. X-rays: ​X-ray has risk of cancer and cell damage. Lead shielding, Monitor exposure (film badge), protective clothing can be used to prevent the risk. Gamma rays​: Gamma rays can damage to living cells. The damage can cause mutations in genes and can lead to cancer. Lead shielding, Monitor exposure (film badge) can be used to prevent the risk. d) Light and sound 3.14 understand that light waves are transverse waves which can be reflected, refracted and diffracted Light waves are transverse wave that is emitted from luminous (objects that emit their own light such as sun, stars, fires, light bulbs etc.) or reflected from non-luminous objects (objects which do not emit their own light but are seen by their reflection of light). Light waves are transverse wave and like all waves, they can be reflected, refracted and diffracted. 3.15 use the law of reflection (the angle of incidence equals the angle of reflection​) The law of reflection states that: i) The incident ray, reflected ray and normal all lie in the same plane. ii) The angle of incidence (ϴi) is equal to the angle of reflection (ϴr). Experiment​: To illustrate the laws of reflection. Apparatus:​ Ray box, strip of plane mirror, protractor, piece of paper. Procedure: 1. Set up the apparatus as shown in Figure. 2. Vary the angle of incidence ​i​ and measure the angle of reflection ​r. ​ nd ​r.​ 3. Compare the values of ​i a 3.16 construct ray diagrams to illustrate the formation of a virtual image in a plane mirror Types of images: i. Virtual images: Image through which the rays of light don’t not actually pass is called virtual image. Example: Image formed in the mirror. Virtual images cannot be produced on a screen. ii. Real images: Images created with rays of light actually passing through them are called real images. Example: cinema screen. Fig. Reflection of a tree. How the virtual image looks like below the lake. Properties of an image in a plane mirror​: The image is as far behind the mirror as the object is in front The is the same size as the object The image is virtualas it appears to be behind the mirror. The rays of light are not actually coming from the place where the image seems to be. The image is laterally inverted – that is, the left side and right side of the image appear to be interchanged. How to construct ray diagrams? Things we include in ray diagrams of a plain mirror: i- Object ii-Observer's eye or some indication iii- Plane mirror iv- Image. 1- Have object infront of the mirror. 2- Draw atleast two rays emanating from the object (one from the top of the object and other at the bottom as shown below) and going towards mirror-- for some objects we need three or more. 3- Reflect ray from the mirror by using law of reflection towards observer. 4- Extend the rays by dotted lines behind the mirror. 5- Construct the image according to the position of the ray ie if ray is coming from the bottom side of the object then it would show the bottom side and so and so as shown below. 3.17 describe experiments to investigate the refraction of light, using rectangular blocks, semicircular blocks and triangular prisms As a light ray passes from one transparent medium to another, it bends. This bending of light is called refraction. Refraction occurs due to having different speed of light in different medium. For example, light travels slower in glass than in air. When ray of light travels from air to glass, it slows down as it crosses the boundary between two media. The change in speed causes the ray to change direction and therefore refraction occurs. Experiment​: To demonstrate the refraction of light through a piece of glass block. Apparatus: ​Rectangular glass block with one face frosted, two rays boxes, piece of paper, protractor. Procedure: 1. Place the glass block on a piece of paper with the frosted side down. 2. Send two narrow rays of light through the glass block as shown in Figure. 3. Observe the paths of the two rays of light. 4. ​ nd measure the angle of refraction​ r ​using Vary the angle of incidence ​i a protractor​. 3.18 know and use the relationship between refractive index, angle of incidence and angle of refraction: The ratio between sine of the angle of incidence and the sine of the angle of refraction is called refractive index. In a material, the refractive index is constant throughout the circuit. sin sin i n= sin sin r sin sin (incident angle) ref ractive index = sin(ref ravted angle) Lighter mediums means that light can pass easily/ speed of light is more. Dense/light doesn’t mean physical density rather than optical condition. Refraction takes place in second medium. The ratio from a vacuum to a denser medium is called absolute refractive index.  The ratio from a medium to another medium is called relative refractive index. It doesn’t have a unit because it is the ratio of same curve. Wavelength decreases in a denser medium, thus decreasing speed. The higher the wavelength, the more the light will bend. The higher the wavelength, the less the angle of refraction. 3.19 describe an experiment to determine the refractive index of glass, using a glass block Experiment​: To determine the refractive index of glass, using a glass block. i. Put the glass block on an wooden table which is passed by a white sheet. ii. The border of the block is marked by a pencil. iii. At one border draw a normal and draw three lines to use as incident ray. iv. Set a ray box through anyone of the lines. v. The ray travels and passes through the glass block and finally emerges from the glass block. vi. The passage of the ray is marked by putting some pins. vii. Now move the glass block and gain the footprints of the pins to show the passage of the ray. viii. Now using a protractor measure the ∠i and ∠r. sin sin i ix. Now using, = sin sin r ; calculate refractive index. Ways to improve result: 1. Repeat the experiment, and find the average reading. 2. Plot a graph of sin I against sin r and find the gradient. 3. Vary the value of i and repeat. 3.20 describe the role of total internal reflection in transmitting information along optical fibres and in prisms Total internal reflection​: When light falls on the surface of a lighter medium from denser medium at an angle of incidence greater than critical angle, then the light does not refracts. It rather reflects in the self-medium. This type of reflection is called total internal reflection. Condition of total internal reflection: 1. Light should fall in the surface of lighter medium from denser medium. 2. Angle of incidence must be greater than the critical angle. Uses of total internal reflection​: i) The prismatic periscope Light passes normally through the surface AB of the first prism (that is, it enters the prism at 90​o​) and so is undeviated. It then strikes the surface AC of the prism at angle of 45​o​. The critical angle for glass is 42​o​ so the ray is totally internally reflected and is turned through 90​o​. On emerging from the first prism the light travels to a second prism which is positioned such that the ray is again totally internally reflected. The ray emerges parallel to the direction in which it was originally travelling. The final image created by this type of periscope is likely to be sharper and brighter than that produced by a periscope that uses two mirrors. Because in mirrors, multiple images are formed due to several partial internal reflections at the non-silvered glass surface of the mirror. ii) Reflectors Reflector is a block of glass that changes the direction of rays into the required position. Light entering the prism undergoes total internal reflection twice. It emerges from prism travelling back in the direction from which it originally came. This arrangement is used in bicycle reflectors and binoculars. iii) Optical fibres Optical fibre uses the property of total internal reflection. This is very thin strand composed of two different types of glass. The inner core is more optically dense than the outer one. As the fibres are narrow, light entering inner core always strike the boundary of the two glasses at an angle greater than critical angle. This technique is used to send information very fast at the speed of light. Optical fibres are also used in endoscopes and telecommunications. The endoscope is used by doctors to see inside human body. Light travels down one bundle of fibres and illuminates the object to be viewed. Light reflected by the object travels up a second bundle of fibres. An image of object is created by the eyepiece. Modern telecommunication systems use optical fibres to transmit messages. Electrical signals from a telephone are converted into light energy by tiny lasers, which send pulses of light into the ends of optical fibres. A light-sensitive detector at the other end changes the pulses back into electrical signals, which then flow into a telephone receiver. Optical fibres allow a much wider bandwidth. This means that many different digital signals can share the same optical fibre, so much more information can be transmitted along an optical fibre than by using an analogue signal. Advantages of sending data using Optical Fibre: Optical fibre is less prone to noise. It is less prone to heating. It can send more information per second than copper wires. 3.21 explain the meaning of critical angle c Critical angle is an incident angle at which the incident ray is refracted and the refracted angle is equal to 90 degree in condition that the light falls on the surface of a lighter medium from denser medium. 3.22 know and use the relationship between critical angle and refractive index: sin sin c = 1n 1 sin sin (critical angle) = ref ractive index 3.23 understand the difference between analogue and digital signals To send a message using a digital signal, the information is converted into a sequence of numbers called a binary code. Digital electrical signals can either have of only two possible values (typically 0v and 5v). These represent the digits 0 and 1 used in the binary number system. In the analogue method, the information is converted into electrical voltages and current that vary continuously. 3.24 describe the advantages of using digital signals rather than analogue signals i. Regenerating digital signal creates a clean accurate copy of the original signal but analogue signal are corrupted by other signals. ii. With digital signal, you can broadcast programs over the same frequency. It is possible because digital signals can carry more information per second than analogue signals. In analogue signal you need wider range of frequency to broadcast. iii. Digital systems are generally easier to design and build than analogue systems. That is the information can be stored and processed by computers. 3.25 describe how digital signals can carry more information Digital signals are capable of carrying more information than analogue signals because digital signals make use of the bandwidth more efficiently by closely approximating the original analogue signal. The parts of the signal that do not carry any information are thrown out thus saving the bandwidth from being used needlessly. Also, depending on the coding process, digital signals are much more efficient at filtering out noise than are analogue signals, which do not filter out noise at all thus saving even more bandwidth. The process of approximating the analogue signal in digital signal processing is called quantization. 3.26 understand that sound waves are longitudinal waves and how they can be reflected, refracted and diffracted Sound waves are longitudinal waves. They are produced by vibration of objects. Like other waves they can also be reflected refracted and diffracted. Reflection​: Sound waves reflect when they bounce back from a surface so that the angle of incident is equal to the angle of reflection. A reflected sound wave is called an echo. Example: Sound is produced behind a nearby wall. After few seconds, a second sound is heard. Due to the reflection of sound wave echo is heard. Refraction​: Sound waves refract when it changes direction while travelling across a high dense medium. Example: Sound wave is sent from the boat to determine the depth of the sea. If refracts when it enters into water. The return wave is received by a receiver. Measure the time required we can measure the depth of sea. Diffraction​: Sound waves are diffracted when they spread while travelling through a narrow space such as doorway. Example: Sound is produced in the corridor. When it leaves the corridor, it diffracts. So a person standing at one side can hear the sound. How sound wave travels? When a vibration occurs, it pushes the air molecules around it closer together. This creates a compression. These particl