Edexcel Physics IGCSE Notes 2025 PDF

PHYSICS I.G.C.S.E Notes 2025 Mohammed Allam Edexcel  Dedication To my obliging assistants: Shahd Mamdouh Sama Mohammed Tasneem Farrag Jana Nader Toqa Mohammed I sincerely appreciate your great efforts and...

PHYSICS I.G.C.S.E Notes 2025 Mohammed Allam Edexcel  Dedication To my obliging assistants: Shahd Mamdouh Sama Mohammed Tasneem Farrag Jana Nader Toqa Mohammed I sincerely appreciate your great efforts and consideration over the years. H ope you accept my thanks.  PHYSICS IGCSE Physics Equations Unit 1 - Mechanics Mohammed Allam  PHYSICS IGCSE Unit 1 - Mechanics Unit 2 - Thermal Mohammed Allam  PHYSICS IGCSE Unit 3 - Waves Unit 4 - Electricity Mohammed Allam  PHYSICS IGCSE Unit 6 - Astronomy Mohammed Allam  PHYSICS IGCSE Index Unit One: Mechanics Chapter 1 Measurements 2 Chapter 2 Kinematics 10 Chapter 3 Forces 17 Chapter 4 Moment 28 Chapter 5 Pressure 30 Chapter 6 Work & Energy 32 Unit Two: Thermal Chapter 1 Kinetic Theory Of Matter 44 Chapter 2 H eat Transmission 51 Chapter 3 H eat Energy 55 Unit Three: Waves Chapter 1 General Properties Of Waves 59 Chapter 2 Sound Waves 64 Chapter 3 Light Waves 68 Mohammed Allam  PHYSICS IGCSE Unit Four: Electricity Chapter 1 Static Electricity 76 Chapter 2 Dynamic Electricity 79 Chapter 3 Electronic Devices 88 Chapter 4 Magnetism 93 Chapter 5 Magnetic Effect of Current 97 Chapter 6 Electromagnetic Induction 105 Unit Five: Atomic Chapter 1 The Nuclear Atom 111 Chapter 2 Radioactivity 114 Chapter 3 Nuclear Reactions 124 Unit Six: Astronomy Chapter 1 Earth & The Universe 133 Chapter 2 Evolution Of The Universe 138 Chapter 3 Stellar Evolution 144 Practical investigations 1-Notes 151 2-Questions 158 Mohammed Allam Unit one: Mechanics PHYSICS IGCSE Unit One Mechanics Mohammed Allam 1 Unit one: Mechanics PHYSICS IGCSE Chapter 1: Measurements Measuring length: Instruments: Micrometer Vernier caliper Ruler (up to 30cm with accuracy 0.1cm) Meter ruler (up to 1m with accuracy 0.1cm) Measuring tape (distance more than 1m with accuracy 1cm) Techniques: Measuring the diameter of a sphere or curved lengths is done by using two wooden blocks. For accuracy: Avoid parallax error by viewing perpendicular to instrument scale. Repeat and take the average result. Vernier Caliper Micrometer Mohammed Allam 2 Unit one: Mechanics PHYSICS IGCSE Measuring volume: Volume: is the space occupied by a body. Volume is measured in m³ or cm³ or mm³. For regular shapes: we use ruler to find dimensions of the body and geometric rules to find the volume (cube, cuboid, cylinder, sphere). For irregular shapes: we use the displacement method. 1. Put some liquid in a measuring cylinder and measure its volume V1 2. Insert the solid gently in the measuring cylinder so that it becomes totally submerged and measure volume V2 of the solid and liquid. 3. The volume of the solid is V= V2 - V1 For accuracy: 1. The measuring cylinder must be vertical by putting it on a horizontal bench. 2. You should view perpendicular to any scale to avoid parallax error. 3. The reading should be taken at the bottom of the meniscus of the water surface. Mohammed Allam 3 Unit one: Mechanics PHYSICS IGCSE Measuring mass: Mass: the amount of matter inside a body. Mass is measured in Kg or g or mg. Mass of a body is always constant. We use spring balance or two pan balance to measure mass. To find mass using spring balance, the reading must be divided by the value of gravity (10). Spring Balance Measuring time: Time is measured in seconds or minutes or hours. We use a clock or a stopwatch to measure time. To increase accuracy of measuring for oscillations, measure time for a number of oscillations from a fixed position and find the average. We can also use light gates to measure time. When the ball passes through a light gate, it cuts a beam of light activating sensors allowing the computer to measure the time taken by the ball to pass through the gate. Mohammed Allam 4 Unit one: Mechanics PHYSICS IGCSE Accuracy vs precision: Precise results don’t necessarily mean accurate results. Accuracy refers to how close a measurement is to the true or accepted value. Precision refers to how close measurements of the same item are to each other. Density: -It is mass per unit volume. ρ: density (Kg/m³ or g/cm³) m: mass (Kg or g) V: volume (m³ or cm³) Density is a scalar quantity. Density is constant for material, but it can vary by temperature. For an object to float on the surface of a liquid, its density has to be lower than that for the liquid, otherwise it will sink. Q: Suggest why solids & liquids have higher densities than gases. A: Because in solids & liquids, atoms are closely packed together so there is a lot of mass in a small volume, unlike gases. Mohammed Allam 5 Unit one: Mechanics PHYSICS IGCSE Basic physical quantities: Quantity Unit (SI) Length Metre (m) Mass Kilogram (kg) Time Second (s) Temperature Kelvin (k) Vector & scalar quantities: Scalars Vectors They have magnitude only They have magnitude & direction Distance Displacement Time Mass Weight Speed Velocity Temperature Acceleration Work & energy Force Density Momentum Power Moment Pressure Mohammed Allam 6 Unit one: Mechanics PHYSICS IGCSE Basic unit conversions: Mass Length g ÷1000 → Kg km ×1000 → m cm ÷100 → m mm ÷1000 → m Time day ×24×60×60 → second hour ×60×60 → second minute x60 → second millisecond ÷1000 → second Other units conversions: current voltage MV ×1,000,000 → V kA ×1000 → A kV ×1000 → V mA ÷1000 → A mV ÷1000 → V energy power MJ ×1,000,000 → J MW ×1,000,000 → W kJ ×1000 → J kW ×1000 → W mJ ÷1000 → J mW ÷1000 → W charge MC ×1,000,000 → C kC ×1000 → C mC ÷1000 → C Mohammed Allam 7 Unit one: Mechanics PHYSICS IGCSE Proportionality: Directly Proportional Inversely Proportional x and y increase or decrease If x decreases, y increases by the together by the same rate. same rate. Meaning that if x is Meaning that if x is halved so does doubled, y will be halved. y and if x increases 4 times, y also increases 4 times. To know if two values are inversely To know if two values are directly proportional or not. Multiply multiple proportional or not. Divide multiple values of x & y, if they always equal values of x & y, if they always equal the same number (constant) then the same number (constant) then they are. they are. X 10 20 25 35 X 2 4 5 10 Y 2 4 5 7 Y 50 25 20 10 div. 5 5 5 5 prod. 100 100 100 100 These two variables are directly These two variables are inversely proportional because we get the proportional because we get the same constant every time. same constant every time. X 10 30 60 100 X 1 3 4 5 Y 5 15 20 25 Y 30 25 20 10 div. 2 2 3 4 prod. 30 75 80 50 Here, the division of the two values Here, the multiplication of the two is not constant therefore these two values is not constant therefore variables are not directly these two variables are not proportional even though the two inversely proportional even though values increase. In this case it’s x increases & y decreases. In this called positive correlation. case it’s called negative correlation. Mohammed Allam 8 Unit one: Mechanics PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 9 Unit one: Mechanics PHYSICS IGCSE Chapter 2: Kinematics Speed & velocity Speed: It is the distance moved per unit time (scalar quantity) Velocity: It is displacement per unit time (vector quantity) v : speed (m/s) d : distance (m) t : time (s) Average speed: For complete journey: For certain set journey with uniform acceleration in straight line: -v: Final speed -u: Initial speed Acceleration: It’s the change of velocity per unit time. Unit for acceleration: m/s² Acceleration of a free fall is approximately 10m/s² Types of acceleration: ○ Body speeding up (+ve acceleration) ○ Body slowing down (-ve acceleration / deceleration) ○ Body changing direction Mohammed Allam 10 Unit one: Mechanics PHYSICS IGCSE Stopping distance: When you’re driving your car & notice that there’s a hazard ahead of you, the first thing you will do is apply the brakes. The distance the car moves before it stops is called the stopping distance. Stopping distance is the sum of your thinking distance & the braking distance. Thinking distance: it’s the distance travelled by the car while you react to the hazard ahead. It takes time for you to take your foot off the accelerator & apply the brakes. Factors that affect the stopping distance: Thinking distance Braking distance Condition of the driver Speed of the car -Sober/drunk/tired Mass of the car Speed of the car Type of the road Visibility of the road -slippery/high friction -clear/foggy Braking system of the car Mohammed Allam 11 Unit one: Mechanics PHYSICS IGCSE Gradient of graphs Gradient of a line is the inclination towards the y-axis. The more the line is inclined towards the y-axis, the steeper it is. Therefore: the steeper the line, the greater the gradient. Gradient Gradient Gradient Gradient = is is is zero constant increasing decreasing Gradient Gradient Gradient is is is constant increasing decreasing But how is this related to physics? Let’s see. Mohammed Allam 12 Unit one: Mechanics PHYSICS IGCSE Distance-time graphs: Y-axis represents distance travelled. X-axis represents the time. The gradient represents speed. Gradient is Gradient is Gradient = 0 Gradient is constant. increasing. Speed = 0 decreasing So the body (curve is So the body (curve is is moving with getting is at rest. getting less constant steeper) steep) speed. So the body So the body is moving with is moving with increasing decreasing speed. speed. Mohammed Allam 13 Unit one: Mechanics PHYSICS IGCSE Speed-time graphs: Y-axis represents speed. X-axis represents time. The gradient represents the acceleration. Area under the graph represents distance travelled. Speed=zero Speed is Speed is Speed is So body is at constant increasing increasing rest Gradient = zero Gradient is Gradient is Gradient = zero So acceleration constant. increasing. So acceleration =zero So the body is So the body is =zero moving with moving with constant increasing acceleration. acceleration. Speed is Speed is Speed is Speed is increasing decreasing decreasing decreasing Gradient is Gradient is Gradient is Gradient is decreasing. constant. increasing. decreasing. So the body is So the body is So the body is So the body is moving with moving with moving with moving with decreasing constant increasing decreasing acceleration. acceleration. acceleration. acceleration. Note: The -ve & +ve in speed determines the direction in which the body is moving. Mohammed Allam 14 Unit one: Mechanics PHYSICS IGCSE Calculating the acceleration from the speed-time graphs: The gradient of the graph represents the acceleration thus, by finding the gradient we find the value of acceleration. Example 1: when the acceleration is constant (straight line) To calculate the gradient we must have 2 points and their x,y coordinates. For this line we will use points A(1,5) & B(2,10) Example 2: when the acceleration is not constant. (curve) Here the examiner has to specify at which time exactly he wants the acceleration because it is changing over time. We can get the acceleration at a specific time by drawing a tangent on the part of the graph corresponding to that time and find the gradient of this line. Find the acceleration at 2 seconds. we will use points A(1,6) & B(2,9) Mohammed Allam 15 Unit one: Mechanics PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 16 Unit one: Mechanics PHYSICS IGCSE Chapter 3: Forces Forces are vector quantities and are measured in Newton. Forces can 1. Change the shape of a body. 2. Change the speed of a body. 3. Change the direction of a body. There are two types of forces. 1. Contact force: forces which act on bodies only. 2. Non-contact force: gravitational force, electric & magnetic force. Properties of common forces: 1. Weight (force of gravity) It’s the Pull of gravity on a body. - w: weight (N) - m: mass (Kg) - g: gravitational field strength (N/Kg) Gravitational strength is constant for each planet (earth=10m/s²) Weight of a body is always drawn vertically downwards from a point called the centre of gravity of the body. If only weight is acting on two bodies released from a high point, they will have the same speed as they fall even if one body is heavier than the other one. (Free Falling) Mass Weight Amount of matter inside a body. Pull of gravity on a body. Scalar quantity. Vector quantity. Measured in Kg. Measured in newton. Has the same value anywhere in Varies from one planet to another the universe. due to change in gravitational strength. Mohammed Allam 17 Unit one: Mechanics PHYSICS IGCSE 2. Normal contact force: This is the force experienced by an object when it pushes against a solid surface. The normal contact force is always drawn perpendicular to the solid surface at point of contact. 3. Lifting force: Any body immersed in a fluid (liquid or gas) experiences an upthrust force called lift. 4. Friction force: Force experienced by an object when it slides or tries to slide on rough surface, it always opposes the direction of motion. It depends on: i) Type of surface. ii) Weight of the body. 5. Drag force: This is a friction force which resists the body through fluids. (liquid or gas) (ex. air resistance, water resistance) The drag is always opposite to the direction of motion. It depends on: i) Speed of the body. ii) Surface area exposed to the fluid. iii) Type of fluid. Mohammed Allam 18 Unit one: Mechanics PHYSICS IGCSE Calculation of resultant force: Resultant force: a single force that has the effect of all forces combined. Fnet = 2+4=6N Fnet = 5-2=3N To the right Fnet = 3-2=1N To the right Upwards Fnet = 5+3=2N Fnet = 3-3=0N To the left N.B: Forces in the direction of motion are called Driving forces. Forces against the direction of motion are called Resistive forces. Mohammed Allam 19 Unit one: Mechanics PHYSICS IGCSE Newton’s laws of motion Three laws that describe the effect of forces on objects Newton’s 1st law: Balanced forces When the resultant force acting on an object is zero, the forces are balanced and the object doesn’t accelerate. It means that it’s either stationary or moving at a constant speed in one direction. 𝐹𝑛𝑒𝑡 = 𝑧𝑒𝑟𝑜 Newton’s 2nd law: Unbalanced forces The net force acting on the body is equal to the product of its mass and acceleration. When the resultant force isn’t equal zero, an unbalanced force is acting on the object, so it accelerates. (speeds up, slows down or changes its direction) 𝐹𝑛𝑒𝑡 = 𝑚𝑎 1. If Driving force > Resistive force ➔ Resultant in the direction of the motion (body accelerates/speeds up). 2. If Driving force < Resistive force ➔ Resultant against the direction of the motion (body decelerates/slows down). 3. If Driving force = Resistive force ➔ Resultant = 0, so the body continues in its state (no acceleration). [Newton’s 1st law] Newton’s 3rd law: To every force there’s an equal & opposite force. F1 = -F2 Ex: when you walk, you push the ground backwards so it pushes you forwards. Mohammed Allam 20 Unit one: Mechanics PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 21 Unit one: Mechanics PHYSICS IGCSE Parachute motion & terminal velocity: 1.When the body is first released, the starting velocity is 0m/s. So there’s no drag & the fnet acting downwards is the weight of the body so the body is accelerating by gravity. 2.Body starts moving (speed increases) so drag force acting against it increases & fnet decreases & acceleration decreases. 3.The body reaches a point where drag increases until it exactly balances out the weight force. Acceleration=0 & fnet=0 So object moves with constant speed (terminal velocity) 4.Parachute opens, increasing the drag, so net force is now acting upwards causing the object to decelerate. 5.As the object slows down, drag decreases until it’s equal to the weight again. fnet=0 , acceleration=0 & the body moves at a constant speed. (another terminal velocity but slower than the 1st one) Mohammed Allam 22 Unit one: Mechanics PHYSICS IGCSE Stretching Elastic force: Deformation means change in shape. Elastic deformation: body returns to it is original shape when the force causing deformation is removed. Plastic deformation: body does not return to it is original shape when the force is removed. Relation between force & extension: Record length of an unstretched spring. Add a load of known mass. Record length of the stretched spring. Repeat the experiment and plot a graph of load against extension. Hooke’s law: Extension is proportional to the force up to the limit of proportionality. It is represented by a straight line passing through the origin. - F: force applied to the spring (N) - x: extension (cm or mm) - k: spring constant (N/cm or N/mm) 𝐹 = 𝑘𝑥 N.B: The spring constant (stiffness) is the gradient of the straight line until the limit of proportionality and it depends on characteristics of the spring. Mohammed Allam 23 Unit one: Mechanics PHYSICS IGCSE Momentum Momentum: It is a vector quantity that is used to explain the results of collisions between objects. What happens to a moving object involved in a collision depends on two factors: the mass of the object and its velocity. Conservation of momentum: Everything that moves has momentum and exerts a force on anything that it interacts with. The law of conservation of momentum states that: When 2 bodies collide, their sum of momenta is the same after the collision as it was before. ○ This is because one body loses momentum while the other body gains momentum by the exact same amount. The changes in momentum are equal in size and opposite in direction. Mohammed Allam 24 Unit one: Mechanics PHYSICS IGCSE Case 1: bodies bounce away Case 2: bodies stick together: from each other: Example: Example: Note: we added a negative sign to v2 Note: the negative sign means that the because it was moving in the opposite ball moved in the opposite direction. direction from v1. The final answer is Therefore, the ball is now moving with positive meaning the bodies are now speed 6.5m/s to the left. moving to the right. Case 3: explosion: Explosion is when two bodies are in contact and one moves away from the other. When 2 bodies are at rest their momentum is zero (because their speed = zero). Therefore, their momentum after explosion should also equal to zero. ➔ Thus, if body 1 moved to the right then body 2 would move to the left with the same amount of momentum to allow the summation of momenta to remain zero. m1v1=(-)m2v2 Mohammed Allam 25 Unit one: Mechanics PHYSICS IGCSE Q: Use ideas about momentum to explain why a skater slides backwards when she throws a snowball forwards. A: According to the law of conservation of momentum, the sum of momenta of the girl & the snowball should always be equal & opposite. The initial momentum is zero but the ball gains momentum when it’s thrown, so the girl has to gain the same amount of momentum in the opposite direction. notice how this is the same concept as Newton's 3rd law? Momentum and Newton’s second law Newton’s second law can be written as follows: The resultant force F that acts on a body depends on how big the change in momentum it experiences and depends also on the time taken to experience the change in momentum. Q: Explain how seat belts/airbags/crumple zones reduce injuries during a car crash. A: They elongate the time of the impact so momentum is reduced over a longer period of time. Force acting on pedestrians decreases when the change of momentum is constant. Mohammed Allam 26 Unit one: Mechanics PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 27 Unit one: Mechanics PHYSICS IGCSE Chapter 4: Moment Moment: is the turning effect of the force around a fixed point. Moment of a force(M) = Force x Perpendicular distance from pivot. Moment is vector quantity (clockwise & anticlockwise direction). - M : moment (N.m or N.cm) - F: force (N) - d: Perpendicular distance of force from pivot (m or cm) Rotating anticlockwise Principle of moments: If an object is to be balanced on a pivot then the sum of clockwise moments must be equal to the sum of anticlockwise moments. At equilibrium Mohammed Allam 28 Unit one: Mechanics PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 29 Unit one: Mechanics PHYSICS IGCSE Chapter 5: Pressure Pressure: It is force per unit area. It is a scalar quantity measured in Pascal. - P: pressure (Pa) - F: force exerted (N) - A : area (m²) Pressure is inversely proportional to the area where the same force is acting. Objects with small surface area have high pressure on the surface they are acting on like: nail, pin & knife. Pressure in liquids: A liquid exerts pressure on the sides and the base of its container. - P: pressure (Pa) - ρ: density (kg/m²) - g: gravitational strength (10 m/s²) - h: depth below surface of the liquid (m) In figure 1, the pressure at point y is greater Than at point x because its height beneath beneath water is greater. The pressure at point y is equal to: Atmospheric pressure + water pressure ρ𝑔ℎ (in air) + ρ𝑔ℎ (in water) N.B: Atmospheric pressure is measured by a barometer. Notes: Mohammed Allam 30 Unit one: Mechanics PHYSICS IGCSE …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 31 Unit one: Mechanics PHYSICS IGCSE Chapter 6: Work & Energy Work done It is product of force and parallel distance moved by the force. Work done is a scalar quantity measured in Joules. - W : work done (J). 𝑊 = 𝐹 × 𝑑moved - F: force exerted on a body (N). - d: distance moved by the body along the direction of force (m). Types of Energy: 1. Potential energy: Energy stored inside a body in many forms. ○ Gravitational potential energy: It is the work done to raise a body to height (h). - g.p.e: gravitational potential energy (J). - m: mass of the body (Kg). - g: gravitational strength (10m/s²). - h: height above the ground (m). 𝑔. 𝑝. 𝑒 = 𝑚 × 𝑔 × ℎ ○ Chemical energy: any chemical reaction involves conversion of chemical energy to some other form of energy. Ex: energy stored in a battery. Mohammed Allam 32 Unit one: Mechanics PHYSICS IGCSE ○ Strain energy: energy gained by a body when experiencing elastic deformation due to stretching, compression, bending or twisting. Ex: energy in a spring. 2. Heat energy: Form of energy that is transferred by difference in temperature. 3. Kinetic energy: Energy due to motion. - K.E : kinetic energy (J). - m: mass of moving body (Kg). - v: speed of the body (m/s). 4. Electrical energy: Energy gained by a charge when passed through conductors or appliances. 5. Internal energy: Energy of molecules in a body (increased when temperature increases). There are many more forms of energies like sound energy, light energy etc.. Mohammed Allam 33 Unit one: Mechanics PHYSICS IGCSE The principle of conservation of energy states that: Energy is neither created nor destroyed, it can only be transferred from one form to another. Therefore, the amount of energy always remains the same. This is why work done on an object is equal to energy transferred to it. Energy transformations: Input energy Output energy electric motor electric kinetic generator kinetic electric car engine chemical kinetic battery chemical electric microphone sound electric loud speaker electric sound matches chemical heat running man chemical kinetic Mohammed Allam 34 Unit one: Mechanics PHYSICS IGCSE Relation between potential energy and kinetic energy: When a body is released to have free fall acceleration (air resistance is ignored), loss in gravitational potential energy is converted to kinetic energy. That’s because the total mechanical energy of the body has to always be constant. So when the body falls from a point, its height above the earth decreases therefore g.p.e also decreases & k.e has to increase to maintain the same amount of total mechanical energy. However, if we take air resistance into consideration, not all gravitational potential energy will be converted to kinetic energy. That’s because there’s work done against friction with air. Q: A ball of mass 100g is thrown vertically upwards with speed 12m/s. If air resistance is ignored, calculate the maximum height it will reach. A: Mohammed Allam 35 Unit one: Mechanics PHYSICS IGCSE Power: It is the rate of transferring energy. It is scalar quantity measured in watts (J/s) - P: Power (W). - W : work done or energy transferred (J). - t: time (s). Efficiency: It is the ratio between useful output to the total input. For example, in a lamp, we want to use the electrical energy input to produce light, but not all the energy input is converted to light, some of it is wasted as heat for example. We calculate efficiency to know how useful an appliance is. Efficiency has no unit. Sankey diagram: It summarises all the energy transfers taking place in a process. The thicker the arrow, the greater the amount of energy involved. The opposite figure is a diagram for a sankey representation of the energy distribution in a lamp. Since the input is the greatest energy value it had to be represented by the thickest line. The total thickness of the other two output lines must add up to be the same as the input. The ratio between the thickness of the two outputs must be the ratio between the two values themselves. Mohammed Allam 36 Unit one: Mechanics PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 37 Unit one: Mechanics PHYSICS IGCSE Energy resources: Renewable: Never runs out. Non-renewable: Has a limited supply & can run out. 1. Fossil fuels: chemical energy stored in fuel is converted to heat energy when burned. This heat energy is used to increase the internal energy of water so it changes into steam & rotates the turbines. The kinetic energy drives generators & is changed to electric energy. Advandatages: Provides a reliable source of power as fossil fuels are readily available. Can be turned on & off at short notice. Disadvantages: Non-renewable energy & we have limited amount of them. Produces gases that contribute to global warming (ex: carbon dioxide). 2. Nuclear power: ○Nuclear fusion: it is the main source of energy in the sun. Light nuclei of hydrogen are combined together to produce a heavier nucleus of helium & a great amount of energy is released. ○Nuclear fission: when a neutron hits a nucleus, it splits into two lighter nuclei. Few neutrons are emitted & large amounts of thermal energy is released & used to vapourize large amounts of water into steam which drives turbines of electric generators. Mohammed Allam 38 Unit one: Mechanics PHYSICS IGCSE Advantages: There’s plenty of nuclear fuel resources so it will last very long. Great amount of energy is released per kilogram of nuclear fuel allowing relatively small amounts of fuel to be transferred. Doesn’t produce gases that contribute to global warming. Disadvantages: Produce radioactive wastes which have a very long half life. Nuclear power is expensive to produce. 3. Wind power: Wind energy generators are driven by giant windmills that convert the kinetic energy into electrical energy. Advantages: It's a clean resource & has no waste products. It's cheap. Renewable resource & will never run out. Disadvantage: It’s unreliable & depends on the weather. Wind turbines cause noise pollution. Wind turbines are unsightly & kill birds. Wind turbines take up lots of space. Mohammed Allam 39 Unit one: Mechanics PHYSICS IGCSE 4. Hydroelectric power: When water rushes from high levels to low levels, gpe is converted to k.e which rotates the turbines & drives generators. Advantages: Reliable resource & has no waste products. Relatively cheap to provide as water is free & doesn’t need mining or transporting. Disadvantages: In the process of building, forests have been cut down causing birds & other animals to lose their habitats. Tidal power can be only used when tides are going out. 5. Solar power: It’s the main energy source on Earth. Solar energy from the sun heats water in solar heaters. Light energy is converted to electric energy in solar cells. Advantages: It's free once solar panels are installed. Renewable & has no waste products. Disadvantages: It's a high initial investment. Unreliable due to weather changes. Cannot operate at night. Mohammed Allam 40 Unit one: Mechanics PHYSICS IGCSE 6. Geothermal power: Geothermal energy that is obtained from hot rocks near the Earth’s surface; the heat energy increases the water’s internal energy so it changes it to steam which rotates turbines & drives generators. Advantages: Renewable & reliable. Has no waste products. Cheap to provide. Disadvantages: Only available in some regions of the geological activity. Requires great expertise. Poisonous gases could be emitted. Mohammed Allam 41 Unit one: Mechanics PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 42 Unit two: Thermal PHYSICS IGCSE Unit Two Thermal Physics Mohammed Allam 43  Unit two: Thermal PHYSICS IGCSE Chapter 1: Kinetic Theory Of Matter Kinetic Theory: The kinetic theory of particles states that: 1. All matter is built up of small particles (molecules). 2. Molecules are in continuous motion as they have kinetic energy. 3. There are intermolecular attraction forces between molecules. 4. There are intermolecular spaces separating molecules. States of matter: State of Shape Arrangement Movement Representation matter and volume Order Spaces Packing Solid Definite Well Very Well Vibrate in shape & ordered close packed place volume Liquid Indefinite Not close Fairly Limited shape ordered packed random free but motion definite Slide past volume each other Gas Indefinite Not Widely Not Total random shape & ordered spaced packed free motion indefinite volume Mohammed Allam 44 Unit two: Thermal PHYSICS IGCSE Changes of state: Melting (Solid to Liquid) Freezing (Liquid to Solid) Boiling (Liquid to Gas) Condensation (Gas to Liquid) Sublimation (Solid to Gas) Deposition (Gas to Solid) Brownian Motion: Smoke particles are present in the air and they move in random directions. Smoke particles are surrounded by thousands of gas molecules that are small & fast, they collide with the smoke particles moving randomly in all directions causing them to move randomly as well. This is called Brownian Motion: The random movement of gas molecules due to colliding with smoke particles that are moving randomly in air. Behaviour of gases: Molecules have kinetic energy because they are moving & potential energy because of the attraction force between them. Temperature: is the average measure of kinetic energy of molecules. Volume of a gas: depends on the spacing between molecules. Pressure of a gas: particles move randomly in all directions, they exert forces on the walls when they make collisions with it; these forces cause pressure on the walls. Mohammed Allam 45 Unit two: Thermal PHYSICS IGCSE Q: Explain how molecules of a gas exert pressure on the inside walls of containers. A: Molecules are in constant random motion so they collide with walls of the container changing their direction & momentum. Since therefore force is exerted on the walls. Hence causing pressure on the walls because Mohammed Allam 46 Unit two: Thermal PHYSICS IGCSE 1. Relation between temperature & pressure (constant volume) When temperature increases, kinetic energy of molecules increases and molecules move faster so the rate of collisions with the wall of the container increases; pressure increases and vice versa. Kelvin scale: As the temperature decreases, the kinetic energy of particles decreases, so pressure decreases. It is predicted that at -273°C, the pressure will be zero which means that the particles will stop hitting the walls of the container & stop moving all together. Kinetic energy of particles is directly proportional to temperature in Kelvin. -273°C is the lowest possible temperature so it’s called Absolute zero. The absolute temperature is measured in Kelvin. Pressure & absolute temperature of a fixed mass of a gas are directly proportional as long as volume is kept constant. PαT(k) Mohammed Allam 47 Unit two: Thermal PHYSICS IGCSE Q: Explain what happens to the pressure inside a container when the temperature decreases. A: The pressure decreases as molecules have less kinetic energy & move slower colliding with the walls less frequently, hence less momentum changes, less force & less pressure. 2. Relation between volume & pressure (constant temperature) When volume of a gas decreases or the gas is compressed, molecules will move in a smaller space so the rate of collisions with the walls of the container increases. Hence the pressure on the walls of the container also increases. Pressure & volume of a gas are inversely proportional as long as temperature is kept constant (Boyle's law). Mohammed Allam 48 Unit two: Thermal PHYSICS IGCSE Evaporation: It’s the escape of the highest energy molecules from the surface of a liquid, these molecules having the highest kinetic energy that is sufficient to break bonds with other surrounding molecules. Factors that increase evaporation rate: 1. Increasing the temperature. 2. Increase the surface area. 3. Passing air across the surface. 4. Reducing humidity. Cooling effect of evaporation: The fastest molecules which have the highest kinetic energy escape from the liquid, as a result the average kinetic energy of the remaining molecules are reduced, so the temperature decreases. ★ Kinetic energy of molecules in a gas is directly proportional to Kelvin temperature. Mohammed Allam 49 Unit two: Thermal PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 50 Unit two: Thermal PHYSICS IGCSE Chapter 2: Heat Transmission Heat energy can be transferred from a hot object to a cooler object by 3 ways: 1. Conduction: ➔ It occurs when there’s contact between two objects. When temperature of a solid increases, the kinetic energy of particles in the hot part increases so the particles vibrate and each particle transfers its vibrational energy to neighbouring particles. Conduction in metals: all metals are good conductors. (ex: copper, iron aluminium) ○ They are fast conductors because they have free moving electrons. Conduction in non-metals: non-metals are poor conductors or insulators. (ex:glass, plastics, wood & rubber) ○ They are very slow conductors as one atom can only transfer energy to its immediate neighbours. Liquid and gases are very poor conductors of heat. Vacuum does not conduct heat at all. Mohammed Allam 51 Unit two: Thermal PHYSICS IGCSE 2. Convection currents: ➔ It occurs in liquids & gases. When a mass of liquid ( or gas ) is heated, it expands because the spacing between its molecules increases. Therefore it becomes less dense and moves upwards while the cooler, more dense liquid sinks to take its place and vice versa. This process is repeated several times until all the liquid is heated. This process cannot happen in solids because they cannot move around and exchange places. Mohammed Allam 52 Unit two: Thermal PHYSICS IGCSE 3. Infrared Radiation: The only way that heat energy can transfer through a vacuum is by radiation, this is because radiation involves transfer of heat energy by a group of electromagnetic waves called infrared waves. All hot objects emit infrared radiation. It’s affected by: a. Temperature: The higher the temperature of an object, the more infrared radiation it emits. b. Colour: Dull black is the best absorber & best emitter while shiny silver is the worst absorber of infrared radiation. c. Surface Area: The larger the surface area of the object, the more infrared radiation it emits or absorbs. Mohammed Allam 53 Unit two: Thermal PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 54 Unit two: Thermal PHYSICS IGCSE Chapter 3: Heat Energy When a piece of matter is heated to raise its temperature, the amount of heat energy (Q) that should be given to this piece of matter depends on: The mass of this piece of matter (m) The required rise in temperature (ΔT) Type of the material (the specific heat capacity (c) of the substance) Specific heat capacity (C): It is the amount of heat energy needed to raise the temperature of 1 Kg of an object by 1℃. - Q: energy supplied or gained (J) - m: mass of the body (Kg) - c: specific heat capacity of the material (J/Kg.C°) - ΔT: difference in temperature (C°) Determination of specific heat capacity: Measure the mass of the liquid using an electronic balance. Measure the initial temperature using a thermometer. Start heating the liquid using an electric heater. Measure the final temperature using a thermometer. Use a stopwatch to determine the time taken. Mohammed Allam 55 Unit two: Thermal PHYSICS IGCSE Heating curve for water: For change in temperature (1,3,5) Heat energy supplied increases the average kinetic energy so the temperature increases. For change in state (2,4) Heat energy supplied is being used in breaking bonds between molecules and increasing potential energy of molecules (separate them) and change from state to state. As the kinetic energy of molecules doesn’t change, temperature will be constant. Mohammed Allam 56 Unit two: Thermal PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 57 Unit three: Waves PHYSICS IGCSE Unit Three Waves Mohammed Allam 58 Unit Three: Waves PHYSICS IGCSE Chapter 1: General Properties of Waves Waves are a way to transfer energy through a particle's vibration. Nature of waves Mechanical waves: waves which need a medium to travel. Ex: ripple waves, sound waves. Electromagnetic waves: waves which don’t need a medium to travel. Ex: light waves, gamma rays, etc. Types of waves Transverse wave: particles of the medium vibrate perpendicular to the direction of energy propagation. ★ Consists of crests & troughs. ★ Ex: water waves & light waves. Longitudinal wave: particles of the medium vibrate parallel to the direction of energy propagation. ★ Consists of compressions & rarefactions. ★ Ex: sound waves. Mohammed Allam 59 Unit Three: Waves PHYSICS IGCSE Properties of waves: Amplitude (a): maximum displacement a particle can reach from mean position. Wavelength (ƛ): distance between 2 successive crests or 2 successive troughs OR distance between 2 successive compressions or 2 successive rarefaction. Frequency ( f ): number of cycles (vibrations) per second, measured in Hertz (Hz). Periodic time (t): time needed to complete one cycle (second) T=1/f Wave speed (v): is the speed at which energy is transferred. - v: speed (m/s) - ƛ: wavelength: (m) - ƒ: frequency (Hz) Frequency of the wave is equal to the source producing it. Speed of the wave depends only on the medium travelling through. Wavelength depends on the type of medium and frequency of the source. In the same medium, when frequency of wave decreases, the wavelength increases and vice versa. Particles of the medium only vibrate in their position. They do not move with the wave. Mohammed Allam 60 Unit Three: Waves PHYSICS IGCSE Drawing waves: Rays: arrows which show the direction of wave motion. Wavefronts: imaginary lines which are drawn perpendicular to the ray, distance between 2 successive wavefronts equal to wavelength. Behaviour of waves: All waves can: reflect & refract. 1. Reflection: When waves are reflected, only their direction changes. Their frequency, wavelength & speed do not change. Mohammed Allam 61 Unit Three: Waves PHYSICS IGCSE 2. Refraction: Refraction is the change in speed of a wave when it moves from one medium to another. Frequency doesn’t change. Speed of the wave & its wavelength are directly proportional. Mohammed Allam 62 Unit Three: Waves PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 63 Unit Three: Waves PHYSICS IGCSE Chapter 2: Sound Waves Sound waves are longitudinal and mechanical waves. Sound wave propagates as a series of compressions and rarefactions. 1. Compression: is a region where spacing between molecules decreases, so pressure increases. 2. Rarefaction: is a region where spacing between molecules increases, so pressure decreases. Characteristics of sound Loudness: this is determined by the amplitude of the sound wave. The higher the amplitude, the louder the sound. Pitch: this is determined by frequency of the sound wave. The higher the frequency, the higher the pitch of sound. Range of audible frequencies: the human ear can only detect waves in the range 20Hz to 20KHz. Mohammed Allam 64 Unit Three: Waves PHYSICS IGCSE Speed of sound: The speed of sound in air is 340m/s. Determination of the speed of sound: a) Direct method: 1. Measure distance (d) using a tape meter. (within 200m) 2. Student (x) fires a gun and student (Y) measures time (t) between seeing the flash and hearing the sound. 3. The speed of sound in air is calculated as follows: v=d/t We assume that the flash of light is emitted at the instant of firing the gun as it will take negligible time to reach the other student: this is because light travels much faster than sound. This procedure must be repeated several times and average results are taken. Mohammed Allam 65 Unit Three: Waves PHYSICS IGCSE b) Echo method: 1. Measure distance (d) with a tape meter. (within 100m to distinguish between the sound and its echo). 2. Measure time (t) between making a short pulse of sound and receiving its echo. 3. Speed is calculated as follow: v=2d/t Oscilloscope: An oscilloscope is a device that can measure the frequency of a sound wave. ➔ How to operate the oscilloscope: Connect the oscilloscope to the sound source you want to measure the frequency of. Adjust the oscilloscope to get a steady trace. Adjust the time base to give a minimum of 1 complete wave on the screen. Count the number of squares for 1 wave & multiply it by the time base to find T. Calculate the frequency using F=1/T Q: In the grid above, the time base is 0.002s per square. Find the frequency. A: 1 complete wave is 7 squares so time period = 7 x 0.002 = 0.014s F=1/T = 1/0.014 = 71Hz Mohammed Allam 66 Unit Three: Waves PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 67 Unit Three: Waves PHYSICS IGCSE Chapter 3: Light Waves Electromagnetic waves Properties: 1. They are the only waves which can transfer energy through vacuum. 2. They travel with the same speed in a vacuum (3x10⁸ m/s). 3. They are transverse waves. 4. They behave same way as mechanical waves: they can reflect & refract. Name of radiation Uses Harms Radio Waves Broadcasting & (Highest wavelength) communication (Least frequency) Microwaves Cooking & satellite Internal heating of transmission body tissue Infrared Heaters & night Skin burns vision equipment Visible light Optical fibres & Eye damage from ROYGBIV photography direct exposure Ultraviolet Fluorescent lamps & Cancer & blindness sterilizing equipment Sunburn (tanning) X-rays Observing internal Cell ionization structure of objects Gamma rays Sterilizing food & Cancer & cell (Least wavelength) medical equipment & mutation (Highest frequency) cancer treatment Mohammed Allam 68 Unit Three: Waves PHYSICS IGCSE Reflection of light: It’s when light rays hit a reflecting surface & bounce off. Angle of incidence: angle between the incident ray & the normal to the surface. Angle of reflection: angle between the reflected ray & the normal to the surface. The angle of incidence is always equal to the angle of reflection. Reflection in mirrors: An image of an object can be seen in a mirror due to intersection of the extension of light rays behind the mirror. Properties of images caused by a mirror. Virtual (cannot be displayed on screen) Distance between mirror & object = distance between image & mirror. Mohammed Allam 69  Unit Three: Waves PHYSICS IGCSE Refraction of light: It happens when the speed of light changes because it passes from one medium to another. Angle of incidence: angle between incident ray & normal to the surface. Angle of refraction: angle between refracted ray & normal to the surface. If light falls perpendicular from one medium to another, the speed and wavelength change, but the direction doesn’t change. When light moves from a less dense medium to a more dense one, it refracts towards the normal & vice versa. Refractive index (n) = ratio between speed of light in air (or vacuum) to the speed of light in the other medium. Refractive index has no unit because it’s a ratio. There is a positive correlation between the angle of incidence & the angle of refraction but there’s a direct proportionality between sin(i) & sin(r) Dense medium Less dense medium Slow speed High speed Short wavelength Long wavelength Mohammed Allam 70 Unit Three: Waves PHYSICS IGCSE How to determine the refractive index of a glass block: 1. Set up a ray box. 2. Position a rectangular block. 3. Mark the path of light rays using pins. 4. Trace around the block then remove it. 5. Use a ruler to draw the rays where the incident ray is parallel to the emergent ray. 6. Make normals. 7. Measure the angle of incidence & angle of refraction. 8. Calculate the refractive index using. 9. Plot a graph of sin(i) against sin(r) & calculate the gradient. 10. Repeat the experiment multiple times & take the average result. Mohammed Allam 71 Unit Three: Waves PHYSICS IGCSE Total internal reflection: All light rays are reflected inside the medium instead of being refracted. It happens when the light is passing from a dense medium to a less dense one with an angle of incidence that is more than the critical angle of the medium. Critical angle: angle of incidence in the denser medium for which the angle of refraction is 90°. Applications on T.I.R: 1. Optical fibres: A very long tube made of glass or plastic. Based on the idea of total internal reflection. Used in making communication lines & material endoscopes. We often use many fibers to produce more detailed images with greater resolution. 2. Periscope (reflecting prism): Used in submarines so people below the water surface can see above. Mirrors or glass prisms (45-45-90) could be used. It depends on the idea of total internal reflection. Mohammed Allam 72 Unit Three: Waves PHYSICS IGCSE Dispersion of light: Monochromatic light has a single wavelength. White light consists of a continuous range of wavelengths that include all wavelengths of the visible light spectrum (ROYGBIV) & some wavelengths in the non-visible regions of the electromagnetic spectrum (infrared & ultraviolet) A beam of white light will be dispersed upon entering a glass prism because the glass has slightly different refractive index values for different colors. Red has the highest speed while violet has the lowest. Red has the lowest refractive index while violet has the highest one. Red light Violet light Longest wavelength Shortest wavelength Highest speed Lowest speed Lowest R.I Highest R.I Mohammed Allam 73 Unit Three: Waves PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 74 Unit four: Electricity PHYSICS IGCSE Unit Four Electricity Mohammed Allam 75 Unit four: Electricity PHYSICS IGCSE Chapter 1: Static Electricity Electric charge: They are 2 types: positive & negative. Like charges repel each other while unlike charges attract each other. Charges come from inside an atom. An atom is electrically neutral as the number of positive protons is equal to the number of negative electrons so they balance out. Methods of charging a body: 1. Charging by conduction: When a charged body touches an uncharged body, the two bodies share the same type of charge. 2. Charging by rubbing: When 2 insulators are rubbed together, they become electrically charged. This is because friction causes free electrons to move from one object to another. The object that lost electrons becomes positively charged while the one that gained electrons becomes negatively charged. Mohammed Allam 76 Unit four: Electricity PHYSICS IGCSE Electric conductors: Materials that contain free electrons flowing through them. ➔ Metals are the best conductors as they have free electrons. Electric insulators: Materials which contain no free electrons. ➔ An insulator should be perfectly dry, moisture can destroy the insulation by conducting electric charges. Properties of a charged body: A body becomes positively charged when it loses electrons and it becomes negatively charged when it gains electrons. Charged bodies attract light objects like dust, small pieces of paper. Like charges repel, unlike charges attract. Applications on electrostatics: 1. Photocopying The ink is negatively charged while the paper is positively charged so the ink is attracted to the paper. 2. Electrostatic paint spraying The spray is negatively charged while the object is positively charged. The spray droplets are attracted by the object & when it’s completely coated, the paint is repelled from the object so it’ll be evenly coated. Mohammed Allam 77 Unit four: Electricity PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 78 Unit four: Electricity PHYSICS IGCSE Chapter 2: Dynamic Electricity The electric current: When a circuit is closed, electrons are repelled from the negative pole of the battery to the positive pole. Conventional current is assumed as if (+) charges are moving in the conductor so it is always opposite to the direction of flow of electrons. Electric current: amount of charge flowing in the circuit per unit time, measured in amperes. (high current means a lot of charge is flowing through the circuit.) I: electric current (A) Q: charge (C) t: time (s) An ammeter is used to measure the electric current in a circuit. It is connected in series with the electric component we want to measure the current flowing through. There are 2 types of current: Direct current (d.c): The current has a constant direction that is represented in the circuit by an arrow. Alternating current (a.c): The current changes directions many times in a second. (it has a frequency of 50Hz) Mohammed Allam 79 Unit four: Electricity PHYSICS IGCSE Voltage It is the energy transferred for each unit of charge that passes through an electrical component. It is determined by the battery or the power source in the circuit. ex: if the battery has 12 volts then the voltage in the circuit is 12 volts. V : voltage (V) E : energy (J) Q: charge (c) A voltmeter is used to measure the voltage in a circuit. It is connected in parallel with the electric component we want to measure the voltage of. Resistance: R: resistance of the component, measured in Ohms (Ω) Resistance of a metal wire depends on: 1. Its length ○ As the length increases, the resistance increases & vice versa (directly proportional) 2. Its cross sectional area ○ As the area increases, the resistance decreases & vice versa (inversely proportional) 3. Its temperature ○ As the temperature increases, the resistance increases. 4. Its material Mohammed Allam 80 Unit four: Electricity PHYSICS IGCSE Variable resistor: Variable resistor also known as rheostat is an example of changing the length to change the resistance hence control the current flowing in the circuit. As the length of the metal bar increases, resistance increases hence current decreases. Ohm’s Law: The voltage across any Ohmic resistor is directly proportional to the current passing through it at a constant temperature. V : voltage (V) I: electric current (A) R : resistance (Ω) Since the voltage & the current are directly proportional, therefore the resistance across an ohmic resistor is constant. (gradient = resistance) Mohammed Allam 81 Unit four: Electricity PHYSICS IGCSE When it comes to non-ohmic resistors, for example a filament lamp, the temperature is not constant as the lamp heats up. Therefore, the resistance increases. Circuit connections: Filament Lamp Series Connections Parallel Connections Advantages: Advantages: Fewer wires. Components receive full Uses lower resistance values voltage of the battery. so it’s cheaper. Components can be Disadvantages: independently controlled. Components get less voltage. Lower overall resistance. Components can’t be Disadvantages: independently controlled. Uses many wires. Voltage of the components Voltage of each component is add up to the voltage of the the same as the voltage of the battery. battery. Current in each component is Current in the components the same as in the whole add up to the current in the circuit. whole circuit. Resistance of the Connecting more resistances components add up to the decreases total resistances of resistance of the whole circuit. the circuit. Mohammed Allam 82 Unit four: Electricity PHYSICS IGCSE Electric energy: It is work done to move charge through voltage. E : Energy (J) V : Voltage (V) I: electric current (A) t: time (s) Power: It is the energy supplied per second. (measured in watts).. ,, Mohammed Allam 83 Unit four: Electricity PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 84 Unit four: Electricity PHYSICS IGCSE Electrical installations: Live wire: carries electrical energy from the power station. Neutral wire: completes the circuit to the station. Earth wire: connected to the metal case of an appliance. Sources of dangers of electricity: Electric shocks can happen due to damaged insulation. A fire can happen if extremely high current passes in the wires, causing them to overheat. Humidity & wet weather reduce resistance of insulators causing it to break its insulation. Electrical devices which have metal cases (ex: refrigerators and washing machines) will cause an electric shock if a bare (not covered) wire makes contact with its metal case. Mohammed Allam 85 Unit four: Electricity PHYSICS IGCSE Methods to protect against dangers of electricity: 1. Earthing 2. Fuses 3. Circuit breakers 1. Earthing: An earth wire is connected to the metal case of the appliance. If the metal becomes charged, the charge will flow into the earth because it has a lower resistance value. This prevents current from passing through people touching the appliance hence protecting them against electric shocks. 2. Fuse: It’s a small glass tube containing a thin wire. If high current passes through the fuse, the thin wire melts and breaks the circuit so no more current can pass. It protects against fires. It’s connected to the live wire. Fuse value should be just above the current in the circuit. 3. Circuit breaker: It’s an electromagnetic switch that opens when current is greater than a certain value. It’s better than a fuse because it’s more sensitive & can quickly reset after a fault. Mohammed Allam 86 Unit four: Electricity PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 87 Unit four: Electricity PHYSICS IGCSE Chapter 3: Electronic Devices 1. Diode: It is a device that allows the current to flow in one direction only. It is made of semiconductors material like germanium or silicon. It is used to change alternating current (A.C) to direct current (D.C) in an electric circuit. It only starts working at 0.6V. From a to b: there is infinite resistance so the current is zero. From b to c: the resistance decreases so current passing increases. Forward Connection Backward connection The diode will be ON. The diode will be OFF. (due to the very high resistance at the negative terminal of the diode.) Mohammed Allam 88 Unit four: Electricity PHYSICS IGCSE Rectification: The diode is used to change the power supply from AC to DC by allowing the current to only pass in the forward direction. Half wave rectification Circuit configuration Input Voltage Waveform After rectification Light emitting diode: Is a diode that emits light when current passes through it (On). It can be used instead of lamps because it’s more efficient as it uses a lower current value for the same brightness hence less energy is wasted. Mohammed Allam 89 Unit four: Electricity PHYSICS IGCSE 2. Thermistor: It’s a device that controls the resistance according to the temperature. Hence controlling the current. As the temperature increases, the resistance decreases. They are used as sensors in fire alarms, ovens, refrigerators, automatic doors, etc. Thermistor 3. Light dependant resistor: It’s a device that controls the resistance according to the light intensity. Hence controlling the current. As the light intensity increases, the resistance decreases. They are used as sensors in street lights. N.B: Both thermistors & light dependent resistors are called sensors & are made of semiconductors. Mohammed Allam 90 Unit four: Electricity PHYSICS IGCSE Glossary of electric circuit symbols: Mohammed Allam 91 Unit four: Electricity PHYSICS IGCSE Notes: …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… …………………………………………………………………………… ………………………………………………………………………….... Mohammed Allam 92 Unit four: Electricity PHYSICS IGCSE Chapter 4: Magnetism Properties of a magnet: It consists of 2 poles (north & south) and both of them attract iron filings. When a magnet is suspended freely, the north pole of the magnet points to the north direction of earth. (compass idea) Like poles repel, unlike poles attract. Magnetic substances: materials which can be magnetised or attracted to magnet Ex: iron (soft) - steel (hard) - cobalt - nickel A soft magnetic material is a material that is easy to be magnetised and demagnetised. A hard magnetic material is a material that is hard to be magnetised and demagnetised. Non-magnetic materials: materials which can't be attracted to magnet (copper, brass, aluminium, wood, plastic, glass, etc..) Mohammed Allam 93 Unit four: Electricity PHYSICS IGCSE Magnetic field: It is the region around a magnet in which a magnetic force is exerted. Magnetic field lines represent magnitude & direction of magnetic field. Field lines are close tog