CIE IGCSE Physics/0625 PDF

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ZNOTES//I GCSESERI ES vi si twww. znot es. org Updat edt o201 9Syl la bus C I EIG CS E P HY SI CS0 62 5 SUMMARI ZEDNOTESON THEEXTENDEDSYLLABUS  TABLE OF CONTENTS 2 CHAPTER 1 General Physics 6 CHAPTER 2 Thermal Physics 9 CHAPTER 3 Properties of waves, including light and sound 13 CHAPTER 4 Electricity and Magnetism 20 CHAPTER 5 Atomic Physics  CIE IGCSE PHYSICS//0625 1. GENERAL PHYSICS DISTANCE TIME GRAPHS 1.1 Length and Time LENGTH A rule (ruler) is used to measure length for distances between 1mm and 1meter. 𝒚 −𝒚 ∆𝑑 For even smaller lengths, use a micrometer screw gauge. 𝑮𝒓𝒂𝒅𝒊𝒆𝒏𝒕 = 𝒙𝟐 −𝒙𝟏 = 𝑡 = Speed (m/s) 𝟐 𝟏 SI unit for length is the meter (m) Therefore, distance: To find out volume of regular object, use mathematical o With constant speed: 𝑆𝑝𝑒𝑒𝑑 × 𝑇𝑖𝑚𝑒 formula o With constant acceleration1: 𝐹𝑖𝑛𝑎𝑙 𝑆𝑝𝑒𝑒𝑑+𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑆𝑝𝑒𝑒𝑑 × To find out volume of irregular object, put object into 𝑇𝑖𝑚𝑒 2 measuring cylinder with water. When object added, it ACCELERATION BY GRAVITY displaces water, making water level rise. Measure this An object in free-fall near to the Earth has a constant rise. This is the volume. acceleration caused by gravity due to the Earth’s uniform TIME gravitational field Interval of time is measured using clocks or a stopwatch Objects are slowed down by air resistance. When SI unit for time is the second(s) deceleration caused by air resistance = acceleration by To find the amount of time it takes a pendulum to make gravity, i.e. no net force acting on a body in free fall, the a spin, time ~25 circles and then divide by the same body reached terminal velocity number as the number of circles. 1.3 Mass and Weight 1.2 Motion Mass: A measure of matter in a body and the body’s Speed is the distance an object moves in a time frame. It resistance to motion. is measured in meters/second (m/s) or kilometers/hour Weight is the force of gravity on a body as a result of its (km/h). mass. 𝑻𝒐𝒕𝒂𝒍 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆 ∴ 𝑺𝒑𝒆𝒆𝒅𝒂𝒗𝒆𝒓𝒂𝒈𝒆 = 𝑾𝒆𝒊𝒈𝒉𝒕 = 𝑴𝒂𝒔𝒔 × 𝑮𝒓𝒂𝒗𝒊𝒕𝒚 𝑻𝒐𝒕𝒂𝒍 𝑻𝒊𝒎𝒆 Speed is a scalar quantity as it only shows magnitude. Weights (and hence masses) may be compared using a Speed in a specified direction is velocity, which is a balance vector SPEED TIME GRAPHS 1.4 Density 𝑴𝒂𝒔𝒔 (𝒎) 𝑫𝒆𝒏𝒔𝒊𝒕𝒚 (𝝆) = 𝑽𝒐𝒍𝒖𝒎𝒆 (𝑽) Density of a liquid: Place measuring cylinder on balance. Add liquid. Reading on measuring cylinder = V, change in mass on balance = m. Use formula. Area under the line equals to the distance travelled Density of solid: 𝑦 −𝑦 ∆𝑣 o Finding the volume: To find out volume of a regular 𝐺𝑟𝑎𝑑𝑖𝑒𝑛𝑡 = 𝑥2 −𝑥1 = 𝑡 = Acceleration (m/s)2 object, use mathematical formula. To find out volume 2 1 Positive acceleration means the velocity of a body is of an irregular object, put object into a measuring increasing cylinder with water and the rise of water is the volume Deceleration or negative acceleration means the velocity of the object. of a body is decreasing o Finding the mass: Use balance A curved speed time graph means changing acceleration. An object will float in a fluid if it’s density is lesser than Acceleration is the rate of change in velocity per unit of the density of the liquid, i.e. The volume of fluid time, and a vector as it’s direction is specified displaced has a greater mass than the object itself. 1 Average Speed * Time PAGE 2 OF 21  CIE IGCSE PHYSICS//0625 Example: an orange with its peel has a Elastic limit: point at which the spring will not return to density of 0.84g/cm3, we can predict that its original shape after being stretched it will float in water because it is less than 𝐿𝑜𝑎𝑑(𝐼𝑛 𝑁𝑒𝑤𝑡𝑜𝑛𝑠) = 𝑆𝑝𝑟𝑖𝑛𝑔 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 × 𝑒𝑥𝑡𝑒𝑛𝑠𝑖𝑜𝑛 1 g/cm3 (density of water). We can also 𝑭 = 𝒌𝒙 say, that an orange without its peel, which has a density of 1.16g/cm3, will sink because it is greater than 1g/cm3. CIRCULAR MOTION An object at steady speed in circular orbit is always 1.5 Forces accelerating as its direction is changing, but it gets no Force is measured in Newtons closer to the center. The speed of the ball stays constant. 𝑭𝒐𝒓𝒄𝒆 = 𝑴𝒂𝒔𝒔 × 𝑨𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 Centripetal force is the force acting towards the center 1 Newton is the amount of force needed to give 1kg an of a circle. It is a force that is needed, not caused, by acceleration of 1m/s2 circular motion, A force may produce a change in size and shape of a For example, when you swing a ball on a string round in body, give an acceleration or deceleration or a change in a circle, the tension of the string is the centripetal force. direction depending on the direction of the force. If the string is cut then the ball will travel in a straight The resultant of forces acting in the same dimension will line at a tangent to the circle at the point where the be their sum, provided a convention for directions is set. string was cut. Therefore, the resultant of 2 forces acting in the same Centrifugal force is the force acting away from the dimension, in the opposite direction will be the center of a circle. This is what makes a slingshot go difference in their magnitude in the direction of the outwards as you spin it. The centrifugal force is the greatest. reaction to the centripetal force. It has the same If there is no resultant force acting on a body, it either magnitude but opposite direction to centripetal force. remains at rest or continues at constant speed in a 1.6 Moments straight line A moment is the measure of the turning effect on a body RESISTIVE FORCES and is defined as: Friction: the force between two surfaces which impedes 𝑴𝒐𝒎𝒆𝒏𝒕(𝑵𝒎) motion and results in heating = 𝑭𝒐𝒓𝒄𝒆(𝑵) × 𝑷𝒆𝒓𝒑𝒆𝒏𝒅𝒊𝒄𝒖𝒍𝒂𝒓 𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝒇𝒓𝒐𝒎 𝑷𝒊𝒗𝒐𝒕(𝒎) Air resistance is a form of friction Therefore, increasing force or distance from the pivot NEWTON’S LAWS OF MOTION increases the moment of a force First law of motion: If no external for is acting on it, an This explains why levers are force magnifiers object will, if stationary, remain stationary, and if o Turning a bolt is far easier with a wrench because the moving, keep moving at a steady speed in the same perpendicular distance from pivot is massively straight line increased, and so is the turning effect. Second law of motion: 𝑭 = 𝒎𝒂 In equilibrium, clockwise moment = anticlockwise Third law of motion: if object A exerts a force on object moment there is no resultant force acting on the body. B, then object B will exert an equal but opposite force on object A o This can be proven by hanging masses of the same HOOKE’S LAW weight on opposite sides of a meter rule on a pivot at Springs extend in equal distances from the pivot showing that the meter proportion to load, as rule in stationary. long as they are under their proportional limit. 1.7 Centre of Mass Limit of proportionality: point at Centre of mass: imaginary point in a body where total which load and mass of body seems to be acting. extension are no longer An object will be in stable equilibrium when it returns to proportional its original position given a small displacement. PAGE 3 OF 21  CIE IGCSE PHYSICS//0625 For an object that is displaced, it will stabilize only if the Conservation of energy: energy cannot be created or force caused by it’s weight is within it’s base. destroyed, when work is done, energy is changed from one form to another. Energy can be stored ENERGY TYPE WHAT IT IS EXAMPLE KINETIC Due to motion Car moving GRAVITATIONAL From potential to fall Book on shelf Bonds in starch CHEMICAL In chemical bonds (food) Stretched elastic STRAIN Compress/stretch band For an object to start rotating it needs to have an Atoms Released in unbalanced moment acting on it NUCLEAR rearranged/split nuclear plant 1.8 Scalars and Vectors INTERNAL Motion of molecules In a glass of A scalar is a quantity that only has a magnitude (so it can water only be positive) for example speed. ELECTRICAL Carried by electrons Battery to bulb A vector quantity has a direction as well as a magnitude, LIGHT Carried in light waves From sun for example velocity, which can be negative. Carried in sound SOUND From speaker Calculating resultant force: waves 𝐾𝑖𝑛𝑒𝑡𝑖𝑐 𝑒𝑛𝑒𝑟𝑔𝑦 = 1⁄2 × 𝑀𝑎𝑠𝑠 × 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 2 𝑲. 𝑬. = 𝟏⁄𝟐 𝒎𝒗𝟐 𝐺𝑟𝑎𝑣𝑖𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 = 𝑀𝑎𝑠𝑠 × 𝐺𝑟𝑎𝑣𝑖𝑡𝑦 × 𝐻𝑒𝑖𝑔ℎ𝑡 𝑮. 𝑷. 𝑬. = 𝒎𝒈𝒉 Example of conversion of energy: A book on a shelf has g.p.e , if it falls of the shelf it will have k.e o A parallelogram has to be made with the acting forces Due to the processes through which energy transfers (F1 and F2). The resultant force will be the diagonal. take place not being 100% efficient, energy is lost to the Make sure the same scale is used to convert between surrounding and therefore energy gets more spread out length and forces. Measure length of diagonal and use (dissipated) scale to convert value into force (FR). Efficiency: how much useful work is done with energy supplied 1.9 Momentum 𝑼𝒔𝒆𝒇𝒖𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 𝒐𝒖𝒕𝒑𝒖𝒕 𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 = × 𝟏𝟎𝟎% Momentum: product of mass and velocity 𝑬𝒏𝒆𝒓𝒈𝒚 𝒊𝒏𝒑𝒖𝒕 𝒑 = 𝒎𝒗 𝑼𝒔𝒆𝒇𝒖𝒍 𝒑𝒐𝒘𝒆𝒓 𝒐𝒖𝒕𝒑𝒖𝒕 𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 = × 𝟏𝟎𝟎% Principle of conservation of linear momentum: when 𝑷𝒐𝒘𝒆𝒓 𝒊𝒏𝒑𝒖𝒕 bodies in a system interact, total momentum remains constant provided no external force acts on the system. 𝒎𝑨 𝒖𝑨 + 𝒎𝑩 𝒖𝑩 = 𝒎𝑨 𝒗𝑨 + 𝒎𝑩 𝒗𝑩 Impulse: product of force and time for which it acts 𝑭𝒕 = 𝒎𝒗 – 𝒎𝒖 1.10 Energy Energy: amount of work and its measured in Joules (J) An object may have energy due to its motion or its position PAGE 4 OF 21  CIE IGCSE PHYSICS//0625 1.11Energy Resources Solar cells/ Renewable sources are not exhaustible photovoltaic Non-renewable sources of energy are exhaustible cells: made of TYPE ADVANTAGES DISADVANTAGES materials that Fuel: burnt to deliver electrical Variable amount Harmful wastes: No CO2 make thermal Cheap current when it produced of sunshine in o Greenhouse/ absorbs light some countries energy, makes Plentiful pollutant gas Solar panels: steam, turns Low-tech o Radiation absorbs energy turbine Wave energy: and use it to heat generators driven water No greenhouse The sun is the source of energy for all our energy by up and down Difficult to build gases produced resources except geothermal, nuclear and tidal motion of waves at sea. In the sun, energy is created through a process called Tidal energy: dam nuclear fusion: hydrogen nuclei are pushed together to form helium. built where river meets sea, lake 1.12 Work and Power fills when tides Expensive Work is done whenever a force makes something move. No greenhouse comes in & Can’t be built 𝑊 = ∆𝐸 gases produced empties when everywhere The unit for work is the Joule (J). tide goes out; 1 joule of work = force of 1 Newton moves an object by 1 water flow runs meter generator Hydroelectric: 𝑾𝒐𝒓𝒌 𝒅𝒐𝒏𝒆 (𝑱) = 𝑭𝒐𝒓𝒄𝒆 (𝑵) × 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆 (𝒎) 𝑾 = 𝑭𝑫 river & rain fill up Low impact on Power is the rate of work lake behind dam, environment Few areas of the The unit for power is Watts (W) water released, Energy produced world suitable 1W = 1J/s turns turbine  at constant rate generator 𝑾𝒐𝒓𝒌 𝑫𝒐𝒏𝒆 (𝑱) 𝑷𝒐𝒘𝒆𝒓 (𝑾) = Geothermal: 𝑻𝒊𝒎𝒆 𝑻𝒂𝒌𝒆𝒏 (𝒔) Deep drilling water pumped No CO2 down to hot rocks produced difficult and 1.13 Pressure expensive Pressure is the force per unit area. rising as steam Nuclear fission: 𝑭𝒐𝒓𝒄𝒆 (𝑵) Produces a lot of 𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆 (𝑷𝒂) = uranium atoms Produces 𝑨𝒓𝒆𝒂 (𝒎𝟐 ) energy with very 𝑭 split by shooting radioactive waste 𝑷= little resources 𝑨 neutrons at them Unit: Pascals (Pa) = N/m2 In Liquids 𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆(𝑷𝒂) = 𝑫𝒆𝒏𝒔𝒊𝒕𝒚(𝒌𝒈/𝒎𝟑 ) × 𝑮𝒓𝒂𝒗𝒊𝒕𝒚(𝒎/𝒔𝟐 ) × 𝑯𝒆𝒊𝒈𝒉𝒕(𝒎) Wind: Windmills 𝑷 = 𝒉𝝆𝒈 are moved by the NO CO2/ Therefore, as the depth of a fluid increases, the pressure breeze. They FEW AREAS OF GREENHOUSE caused by the whole liquid increases. THE WORLD generate GASSES SUITABLE. electricity from PRODUCED kinetic energy. PAGE 5 OF 21  CIE IGCSE PHYSICS//0625 Measuring Pressure: 2. THERMAL PHYSICS MANOMETER BAROMETER 2.1 Simple Kinetic Molecular Model of Matter A manometer measures Tube with vacuum at the SOLID LIQUID GAS the pressure difference. top and mercury filling Fixed shape and Fixed volume but No fixed shape The height difference the rest. volume changes shape or volume, gases shows the excess Pressure of the air pressure in addition to pushes down on Strong forces of depending on its fill up containers the atmospheric reservoir, forcing attraction container Almost no pressure. mercury up the tube. between Weaker intermolecular particles- Measure height of attractive forces forces- large particles close to mercury than solids- distances each other. ~760 mm of mercury is 1 medium between Fixed pattern atm. distances particles (lattice) Atoms vibrate between Particles far but can’t change particels apart, and move position ∴ fixed No fixed pattern, quickly volume and liquids take Collide with each shape shape of their other and container bounce in all Particles slide directions past each other. The more the kinetic energy in a gas, the faster it’s particles move and therefore the gas is at a higher temperature. The pressure gases exert on a container is due to the particles colliding on the container walls. The greater the kinetic energy in gasses the faster they move and the more often they collide on the container’s walls. Therefore, the volume is constant, then increasing the temperature will increase the pressure. Thus, if there is a change in momentum of the particles, the kinetic energy decreases, decreasing the collisions on the container walls and thus the pressure. BROWNIAN MOTION Gas molecules move randomly. This is because of repeated random collisions with other gas molecules, which constantly change the direction they move in. PAGE 6 OF 21  CIE IGCSE PHYSICS//0625 Small molecules move much faster and have higher As the temperature increases of a fixed mass of gas, the energy than larger molecules. They can effectively move pressure increases as the average kinetic energy large molecules due to repeated random bombardment- increases… EXPLAINED IN DETAIL IN 2.1 this can be seen by larger smoke particles moving. Therefore, the random motion of particles in a 2.4 Thermal properties and temperature suspension is evidence for the kinetic molecular model Solids, liquids and gasses expand when they are heated of matter. as atoms vibrate more and this causes them to become further apart, taking up a greater volume. 2.2 Evaporation Due to differences in molecular structure of the different It is the escape of more energetic particles from the states of matter, expansion is greatest in gases, less so in surface of a liquid. liquids and lowest in solids If more energetic particles escape, the liquid contains Applications and consequences of thermal expansion: few high energy particles and more low energy particles o Overhead cables have to be slack so that on cold so the average temperature decreases. days, when they contract, they don’t snap or detach. o Gaps have to be left in bridge to allow for expansion o Bimetal thermostat: when temperature gets too high, bimetal strip bends, to make contacts separate until temperature falls enough, then metal strip will become straight again and contacts touch, to maintain a steady temperature In the above graph, the number of particles with higher kinetic energies has gone down.’ Therefore a body in contact with an evaporating liquid Temperature can be measured by observing a physical with subsequently cool. property that changes with temperature. Examples Evaporation can be accelerated by: include alcohol and mercury - used in thermometers. o Increasing temperature: more particles have energy Fixed points are definite temperatures at which to escape something happens and are used to calibrate a o Increasing surface area: more molecules are close to thermometer. For example, melting and boiling point of the surface water o Reduce humidity level in air (draught): if the air is less Sensitivity: Change in length or volume per degree humid, fewer particles are condensing. Range: The values which can be measured using the thermometer 2.3 Pressure Changes in Gases Linearity: Uniform changes in the physical property with Pressure is inversely proportional to the volume given a a change in temperature over the measured constant temperature. temperature values. If the volume increases and the temperature stays Responsiveness: How long it takes for the thermometer constant, the particles hit the surface less often, thus to react to a change in temperature decreasing the pressure. Calibrating a thermometer: 𝑷𝟏 𝑽𝟏 = 𝑷𝟐 𝑽𝟐 o Place thermometer in melting ice, this is 0 °C. o Place thermometer in boiling water, this is 100 °C. 𝑷𝑽 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕 The constant is valid at a fixed mass of gas at a constant temperature. PAGE 7 OF 21  CIE IGCSE PHYSICS//0625 Liquid-in-glass thermometer: IMPORTANT: The Q’s in both equations are NOT the same, however the c’s are. 2.6 Melting and Boiling Melting is when a solid turns into a liquid. The temperature increases thus kinetic energy in solid o As temperature rises or falls, the liquid (mercury or increases and particles vibrate more rapidly. alcohol) expands or contracts. When melting starts there is no increase in temperature o Amount of expansion can be matched to temperature of the substance because thermal energy supplied is on a scale. being used to break bonds between particles of the solid o To increase sensitivity: thus making it into a liquid. ▪ Thinner capillary The latent heat of fusion is the amount of energy needed ▪ Less dense liquid to melt 1Kg of a substance ▪ Bigger bulb The melting point is the temp. at which a substance boils o Depending on the melting and boiling point of the Boiling is when a liquid turns into a gas liquid being used, the range is defined. o The linearity depends on the liquid being used The temperature increases thus kinetic energy in liquid increases and particles vibrate more rapidly. Thermocouple thermometer: When boiling starts, there is no increase in temperature of the substance because the thermal energy supplied is being used to break bonds between particles of the liquid thus making it into a gas. The latent heat of vaporization is the amount of energy needed to boil 1Kg of a substance o The probe contains 2 different metals joined to form The boiling point is the temp. at which a substance melts 2 junctions. 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐿𝑎𝑡𝑒𝑛𝑡 𝐻𝑒𝑎𝑡 𝑜𝑓 𝐹𝑢𝑠𝑖𝑜𝑛/𝑉𝑎𝑝𝑜𝑟𝑖𝑧𝑎𝑡𝑖𝑜𝑛 = 𝐸𝑛𝑒𝑟𝑔𝑦 𝑇𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑 o The temperature difference causes a tiny voltage 𝑀𝑎𝑠𝑠 𝑬 which makes a current flow. 𝑳𝒇 /𝑳𝒗 = o A greater temp. difference gives a greater current. 𝒎 o Thermocouple thermometers are used for high temperatures which change rapidly and have a large The difference between boiling and evaporation is that: range (-200C° to 1100°C) o Boiling occurs at a fixed temperature and throughout the liquid 2.5 Thermal Capacity: o Evaporation occurs at any temperature and only on The rise in temperature of a body is an increase in the the surface internal energy of that body. The average kinetic Condensation is when a gas turns back into a liquid. energy of a gas particle is directly proportional to When a gas is cooled, the particles lose energy. They the temperature. When of that gas particle. particles move more and more slowly. When they bump into each other, they do not have enough energy to bounce away move faster due to greater kinetic energy, they collide again so they stay close together, and a liquid forms. more often, which is felt by heat When a liquid cools, the particles slow down even more. This relationship is shown by the thermal capacity of a Eventually they stop moving except for vibrations and a Specific Heat capacity (c) is the amount of energy solid forms. required to raise the temperature of 1 kg of a certain substance by 1o C. 2.7 Thermal Properties 𝑄 Conduction is the flow of heat 𝑐= 𝑚 ∆𝑇 through matter from places of higher Thermal Capacity (Q) is the amount of energy required temperature to places of lower to raise the temperature of an object by 1oC. temperature without movement of 𝑄 = 𝑚𝑐 the matter as a whole PAGE 8 OF 21  CIE IGCSE PHYSICS//0625 In non-metals - when heat is supplied to something, its 3. PROPERTIES OF WAVES, INCLUDING LIGHT atoms vibrate faster and pass on their vibrations to the AND SOUND adjacent atoms. In metals – conduction happens in the previous way and 3.1 General Wave Properties: in a quicker way –electrons are free to move, they travel Waves transfer energy without transferring matter. randomly in the metal and collide with atoms and pass on the vibrations Good conductors are used whenever Examples of wave motion include: heat is required to travel quickly through something o Water Waves o Ropes Bad conductors (insulators) are used to reduce the o Springs amount of heat lost to the surroundings Frequency: the number of waves Convection is the flow of heat through a fluid from passing any point per second places of higher temperature in places of lower measured in hertz (Hz) temperature by movement of the fluid itself. 𝟏 As a fluid (liquid or gas) warms up, the particles which 𝑭𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 = 𝑷𝒆𝒓𝒊𝒐𝒅 are warmer become less dense and rise. Period: time taken for one oscillation They then cool and fall back to the heat source, creating in seconds a cycle called convection current. Wavefront: the peak of a transverse wave or the As particles circulate they transfer energy to other compression of a longitudinal wave particles. If a cooling object is above a fluid it will create Speed: how fast the wave travels measured in m/s a convection current as well. Wavelength: distance between a Radiation is the flow of heat from one place to another point on one wave to the by means of electromagnetic waves. It does not require corresponding point on the next a medium. wave in length Thermal radiation is mainly infra-red waves, but very hot Amplitude: maximum objects also give out light waves. Infra-red radiation is displacement of a wave from its part of the electromagnetic spectrum. undisturbed point. MATT BLACK WHITE SILVER EMITTER Best Worst REFLECTOR Worst Best ABSORBER Best Worst An emitter sends out thermal radiation. A reflector reflects thermal radiation, therefore is a bad absorber. An emitter will cool down quickly, an absorber will heat TRANSVERSE WAVES LONGITUDINAL WAVES up more quickly and a reflector will not heat up quickly. The amount of radiation also depends on the surface temperature and surface area of a body. Travelling waves in Travelling waves in Consequences of energy transfer include: which oscillation is which oscillation is o Metal spoon in a hot drink will warm up because it parallel to direction of perpendicular to conducts heat travel. o Convection currents create sea breezes. During the direction of travel Has crests and troughs Has compressions and day the land is warmer and acts as heat source. During rarefactions the night the sea acts as the heat source. For example, light, water For example, sound o A black saucepan cools better than a white one, white waves and vibrating waves houses stay cooler than dark ones. string 𝑆𝑝𝑒𝑒𝑑 (𝑚/𝑠) = 𝐹𝑟𝑒𝑞𝑢𝑛𝑐𝑦(𝐻𝑧) × 𝑊𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ(𝑚) 𝑽 = 𝑭𝝀 PAGE 9 OF 21  CIE IGCSE PHYSICS//0625 Refraction: 3.1 Reflection of Light o Speed and wave length is reduced but frequency Plane (flat) mirrors produce a reflection. stays the same and the wave changes direction Rays from an object reflect off the mirror into our eyes, o Mechanical waves slow down when they pass from a but we see them behind the mirror. denser to a rarer material and vice versa The image has these properties: o Note: Electromagnetic waves like light increase in o Image is the same size as the object speed from an optically denser to a rarer medium. o Image is the same distance from the mirror as object o When wave is slowed down, it is refracted towards o A line joining corresponding points normal (i > r) of the image and object meet the o When wave is sped up, it is refracted away from mirror at a right angle normal (i < r) o Image is virtual: no rays actually o Deep water is denser than shallow water pass through the image and the image cannot be formed on a screen Laws of reflection: o Angle of incidence = angle of reflection o The incident ray, reflected ray and normal are always When water wave travels When water waves on the same plane (side of mirror) from deep to shallow; travel from shallow to Critical angle: angle at which refracted ray is parallel to speed decreases, deep; speed increases the surface of material. wavelength decreases and wavelength increases If the angle of incidence is greater than the critical frequency remains angle there is no refracted ray, there is total internal and frequency remains constant reflection. constant If the angle of incidence is less than the critical angle Reflection: the incidence ray will split into a refracted ray and a o Waves bounce away weaker reflected ray. from surface at same angle they strike it o Angle of incidence = angle of reflection o The incident ray, normal and reflected ray all lie on the same plane. o Speed, wavelength and frequency are unchanged by reflection 𝑺𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒊𝒈𝒉𝒕 𝒊𝒏 𝒗𝒂𝒄𝒖𝒖𝒎 𝑹𝒆𝒇𝒓𝒂𝒄𝒕𝒊𝒗𝒆 𝑰𝒏𝒅𝒆𝒙 = Diffraction: 𝑺𝒑𝒆𝒆𝒅 𝒐𝒇 𝒍𝒖𝒈𝒉𝒕 𝒊𝒏 𝒂 𝒎𝒆𝒅𝒊𝒖𝒎 Waves bend round the 𝐬𝐢𝐧 𝒊 𝑹𝒆𝒇𝒓𝒂𝒄𝒕𝒊𝒗𝒆 𝑰𝒏𝒅𝒆𝒙 = sides of an obstacle, or 𝐬𝐢𝐧 𝒓 spread out as they pass 𝑪𝒓𝒊𝒕𝒊𝒄𝒂𝒍 𝒂𝒏𝒈𝒍𝒆 = 𝐬𝐢𝐧−𝟏 𝟏⁄𝒏 through a gap. Wider gaps produce less diffraction. When the gap size is equal to the wavelength, maximum diffraction occurs PAGE 10 OF 21  CIE IGCSE PHYSICS//0625 3.2 Refraction of Light Real Image Refraction is the bending when light travels from one When object is further away from the optical centre medium to another due to the change in speed of the than F’ is ray of light. Note: o The emergent ray is parallel to the incident ray only if the sides of the glass are A) A ray through centre of the lens passes straight through parallel) the lens. o i = angle of incidence, B) A ray parallel to the principal axis passes through the r = angle of refraction focus on the other side of the lens C) A ray through F’ will leave the lens parallel to the principal axis Light put in at one end is totally internally reflected until Virtual Image it comes out the other end. When the object is closer to the optical centre than F’ is Application: Optical Fibres o Used in communications: signals are coded and sent along the fiber as pulses of laser light o Used in medicine: an endoscope, an instrument used by surgeons to look inside the body; contains a long bundle of optic fibers. 3.3 Thin Converging Lens Magnifying glass: when a convex lens is used like this - Principal focus: the point where rays parallel to the an object is closer to a convex (converging) lens than the principal axis converge with a converging lens. principal focus (like the diagram above), the rays never Focal length: distance from principle focus and the converge. Instead, they appear to come from a position optical center. behind the lens. The image is upright and magnified, it is Principal axis: line that goes through optical center, a virtual image. and the 2 foci. Images can be: Optical center: the center of the lens o Enlarged: The image is larger than the object. Real: image can be caught on a screen o Same size: The image is the same size as the object. Virtual: image cannot be caught on a screen o Diminished: The image is smaller than the object. o Upright: The image is in the same vertical orientation as the object. PAGE 11 OF 21  CIE IGCSE PHYSICS//0625 3.4 Dispersion of Light Applications: Refraction by a prism: o Radio waves: radio and television communications When light is refracted o Microwaves: satellite television and telephones by a prism, the o Safety issue: cause internal heating of body tissues incidence ray is not o Infrared: electrical appliances (radiant heaters and parallel to the grills), remote controllers for televisions and intruder emergent ray, since the alarms prism’s sides are not o X-rays: medicine (x-ray photography and killing cancer parallel. cells) and security If a beam of white light is passed through a prism it is o Safety issue: is a mutagen, it cause cancer (mutations) dispersed into a spectrum. o Monochromatic: light of a single wavelength and color White light is a mixture of colors, and the prism refracts (used in lasers) each color by a different amount – red is deviated least & violet most 3.6 Sound Sound is a mechanical wave. Monochromatic light is that of a single frequency and colour. Sound waves come from a vibrating source e.g. loudspeaker The visible spectrum of light looks like this : As the loudspeaker cone vibrates, it moves forwards and backwards, which squashes & stretches the air in front. As a result, a series of compressions (squashes) and 3.5 Electromagnetic Spectrum rarefactions (stretches) travel out through the air, these are sound waves Humans can hear frequencies between 20 and 20 000Hz. Properties: o Sound waves are longitudinal: they have compressions and rarefactions and oscillate backwards and forwards. o Sound waves need a medium to travel through as it moves due to oscillating particles. Ultrasound Waves: high frequency sound waves, ROMAN MEN INVENTED VERY UNUSUAL XRAY GUNS medically used to look at structures and organs inside the human body, i.e. to form an image of a fetus in a pregnancy All electromagnetic waves: o Travel at the speed of light: approximately 3 × 108m/s. o They travel at around the same speed in air too. o Don’t need a medium to travel through (travel through a vacuum) o Can transfer energy Compression: High pressure section of a longitudinal o Are produced by particles oscillating or losing energy wave in some way Rarefaction: Low pressure section of a longitudinal wave o Are transverse waves The higher the frequency, the higher the pitch. The higher the amplitude, the louder the sound PAGE 12 OF 21  CIE IGCSE PHYSICS//0625 If a sound is repeated 0.1 seconds or more after it is first Methods of inducing magnetism: heard, the brain senses it again. o A piece of steel becomes permanently magnetized Therefore , given the adequate distance, if sound reflects when placed near a magnet, but its magnetism is off a surface, and comes back, an echo is produced. usually weak. o It can be magnetized more strongly by stroking it with SPEED OF SOUND IN VARRIOUS MEDIA one end of a magnet o Most effective method: place it in a solenoid and pass a MEDIUM State Speed large, direct current (d.c.) through the coil. CONCRETE Solid 5000 m/s Methods of demagnetisation: PURE WATER Liquid 1400 m/s o If a magnet is hammered, its atomic magnets are AIR Gas 330 m/s thrown out of line and it becomes demagnetized. 𝑽 𝒊𝒏 𝑮𝒂𝒔 < 𝑽 𝒊𝒏 𝑳𝒊𝒒𝒖𝒊𝒅 < 𝑽 𝒊𝒏 𝑺𝒐𝒍𝒊𝒅 o Heating a magnet to a high temperature also Finding the speed of sound demagnetize it. o When sound reflects off of a wall, it will come back to o Stroking with another magnet to destroy the you; echo alignment of poles o If you know the distance between you and the wall, o Place magnet with poles opposite to that which is and measure how long it takes for the echo to sound, induced by a d.c. current and insert into coil with d.c. you can figure out the speed of sound in air. current o Remember to take into account that sound has gone o Most efficient method: place magnet inside a solenoid there & back connected to an alternating current (a.c.) supply. Soft Iron vs. Steel 4. ELECTRICITY AND MAGNETISM SOFT IRON STEEL 4.1 Simple phenomena of magnetism Gets magnetized Slow to be MAGNETS: faster but loses its magnetized but magnetism as soon retains acquired Magnets have a magnetic field around them as inducing magnet is magnetism for a long They 2 opposite poles (North and South) which exert removed. time. forces on other magnets. Like poles repel and unlike High susceptibility Low susceptibility but poles attract. This is caused by the interaction of but low retentivity high retentivity. magnetic fields. Use: core in the Use: making o Therefore if magnets are facing each other with transformer magnets. opposite poles, they will come together given a small Permanent Magnet vs. Electromagnet space between them PERMANENT MAGNET ELECTROMAGNET They attract magnetic materials by inducing (permanent Design: hard magnetic Design: Uses a solenoid or temporary) magnetism in them. material to create magnetic field Will exert little or no force on a non-magnetic material Use: for applications Use: For applications The direction of an electric field at a point is the where magnetism is where magnetic field direction of the force on a positive charge at that point needed over long needs to be turned on & Induced Magnetism: periods – fridge doors off - scrap metal moving o Magnets attract materials by inducing magnetism in them; the material becomes a magnet as well. o The side of the material facing the magnet will become the opposite pole as the magnet. FERROUS NON-FERROUS Magnetic materials Non-magnetic materials IRON PLASTIC NICKEL WOOD COBALT RUBBER PAGE 13 OF 21  CIE IGCSE PHYSICS//0625 4.2 Electric Charge Induced charges: There are 2 types of charges: positive and negative. o Charging a body involves the addition or removal of Unlike charges attract and like charges repel. electrons. The SI unit of charge is the Coulomb (C). o A charge that “appears” on an uncharged object The presence of an electrostatic charge can be detected because of a charged object nearby using a leaf electroscope. o For example if a positively charged rod is brought near o If a charged object is placed near the cap, charges are a small piece of aluminum foil, electrons in foil are induced. pulled towards rod, which leaves the bottom of the foil o The metal cap gets one type of charge (positive or with a net positive charge. negative) and the metal stem and gold leaf get the o The attraction is stronger than repulsion because the other type of charge so they repel each other. attracting charges are closer than the repelling ones. 4.3 Current Current: a flow of charge, the SI unit is the Ampere (A). An ammeter measures the current in a circuit and is connected in series Current is a rate of flow of charge. In metals, current is caused by a flow of electrons 𝐶ℎ𝑎𝑟𝑔𝑒 (𝐶) 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) = Electric field: region in which electric charge experiences 𝑇𝑖𝑚𝑒 (𝑠) 𝐼 = 𝑄/𝑡 a force. Current follows path of least resistance The direction of an electric field at a point is the Conventional current flows in the direction opposite to direction of the force on a positive charge at that point that which electrons flow in. Conductors: materials that let electrons pass through them. Metals are the best electrical conductors as they have free electrons. E.g. copper Red= Conventional Current Insulators: materials that hardly conduct at all. Their Green= flow of electrons are tightly held to atoms and hardly move, but electrons they can be transferred by rubbing. E.g. Rubber Simple Field Patterns: 1𝑒̅ = 1.6 × 10−19 𝐶 1𝐶 = 6.25 × 1018 𝑒̅ 4.4 Electromotive Force (EMF) The energy supplied by the source in driving a unit Parallel Point +ve and -ve +ve and +ve charge around a circuit. plates charge The maximum voltage a cell can produce is called the electromotive force (EMF), measured in volts. When a current is being supplied, the voltage is lower because of the energy wastage inside the cell. A cell produces its maximum PD when not in a circuit and not supplying current. PAGE 14 OF 21  CIE IGCSE PHYSICS//0625 4.5 Potential Difference (P.D) 4.8 Series and Parallel Circuits Potential difference, or PD for short, is also known as The current at any point in a series circuit is the same voltage. The current splits at each branch in a parallel circuit so Voltage is the amount of energy the cell gives the the total current is always greater than the current in electrons it pushes out. Voltage is measured in volts (V) one branch and is measured by a voltmeter (connected in parallel). If Combining resistors a cell has 1 Volt, it delivers 1 Joule of energy to each o In Series: 𝑹𝑻𝒐𝒕𝒂𝒍 = 𝑹𝟏 + 𝑹𝟐 coulomb of charge (J/C). 𝟏 o In Parallel: 𝑹𝑻𝒐𝒕𝒂𝒍 = 𝟏 𝟏 ⁄𝑹 + ⁄𝑹 𝟏 𝟐 𝑬𝒏𝒆𝒓𝒈𝒚 o The combined resistance of 2 resistors in parallel is 𝑽𝒐𝒍𝒕𝒂𝒈𝒆 = 𝑪𝒉𝒂𝒓𝒈𝒆 less than that of either resistor by itself and the 𝑬 current in the two resistors in greater in the source 𝑽= 𝑪 than in the individual resistors and is equal to the sum of the currents in all the resistors connected in 4.6 Resistance parallel. 𝑽𝒐𝒍𝒕𝒂𝒈𝒆 𝑽 Advantages of putting lamps in parallel are: 𝑹𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 (Ω) = = 𝑪𝒖𝒓𝒓𝒆𝒏𝒕 𝑰 o If one lamp breaks, the other still works Factors affecting resistance: o Each lamp gets maximum PD Length In series: PD across the supply = PD across all the oΩ∝𝐿 components combined o The electrons have to travel a longer length and thus In parallel: Current across the source = sum of currents encounter more resistance. in the separate branches Cross-sectional area 1 oΩ∝ 𝐴 4.9 Circuit Diagrams o More electrons can flow per unit time, increasing the Cell current and therefore decreasing the resistance. Material o Better conductor = less resistance Battery of cells Current Voltage Character of an Ohmic Resistor and a Filament Lamp: Or Power supply o Ohm’s law states that voltage across a resistor is a.c. power directly proportional to the current through it. This is supply only true if the temperature of the resistor or lamp Junction of remains constant conductors Lamp 4.7 Electrical Energy Electrical energy is transferred from the battery or Fixed resistor power source to the circuit components then into the Thermistor surroundings 1 Watt is 1J/s Variable Resistor 𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉) × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) 𝑷 = 𝑽𝑰 Light dependent 𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉) × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 resistor 𝑬 = 𝑽𝑰𝒕 Heater PAGE 15 OF 21  CIE IGCSE PHYSICS//0625 Switch 4.10 Action and Use of Circuit Components: Earth or Ground A potential divider divides the voltage into smaller parts. Electric Bell Buzzer Microphone Loudspeaker To find the voltage (at VOUT) we use the following formula: 𝑹𝟐 Motor 𝑽𝑶𝑼𝑻 = 𝑽𝑰𝑵 × ( ) 𝑹𝑻𝒐𝒕𝒂𝒍 Generator A variable potential divider (potentiometer) is the same as the one above but using a variable resistor; it acts like Ammeter a potential divider, but you can change output voltage. Input Transducers: Voltmeter o Thermistor: input sensor and a transducer. It is a temperature- Galvanometer dependent resistor. At higher Potential Divider temperature there is less resistance. o Light dependent resistor (LDR): input Relay Coil sensor and a transducer. When light intensity increases, resistance Transformer decreases. Relays: Diode o A switch operated by an electromagnet Light- emitting diode Fuse Oscilloscope AND gate OR gate NORMAL CLOSED RELAY NORMALLY OPEN RELAY NAND gate NOR gate NOT gate When coil not energized, When coil energized, switch is closed, switch is closed, completing circuit completing circuit PAGE 16 OF 21  CIE IGCSE PHYSICS//0625 Diodes: 4.12 Dangers of Electricity: o A device that has an extremely high resistance in one Hazards: direction and a low resistance in the other, therefore o Damaged insulation: contact with the wire (live wire it effectively only allows current to flow in one especially) due to gap in the insulation causes electric direction shock which can cause serious injury or shock. o Forward bias is when the diode is pointing in the o Overheating of cables: when long extension leads are direction of the conventional current and reverse bias coiled up, they may overheat. The current warms the is the opposite wire, but the heat has less area to escape from a tight o It can be used in a rectifier; turns AC current into DC bundle. This might cause a fire. current. o Damp conditions: water can conduct a current, so if electrical equipment is wet someone might get electrocuted FUSE CIRCUIT BREAKER 4.11 Digital Electronics A fuse protects a circuit. An automatic switch Analogue uses a whole range of continuous variations to Thin piece of wire which which if current rises over transmit a signal that include variations of high and low overheats and melts if a specified value, the states. current is too high. It is electromagnet pulls the Digital signals use only 2 states, on and off. placed on the live wire contacts apart, breaking Logic gates are processors that are circuits containing transistors and other components. Their function is before the switch. This the circuit. The reset shown by the truth table below (3 columns from the prevents overheating and button is to rest catching fire. A fuse will everything. It works like a right) have a specific current fuse but is better because value (e.g. 13 Amps.) so it can be reset. when choosing a suitable fuse you must use the one above minimum value but less than maxiumum value Benefits of Earthing a Metal Case: o Many electrical appliances, have metal cases, the earth wire creates a safe route for current to flow through if the live wire touches the casing o Earth terminal connected to metal casing, so in such a case, the current goes through earth wire instead of causing an electric shock. o A strong current surges through earth wire because it has very low resistance o This breaks the fuse and disconnects the appliance PAGE 17 OF 21  CIE IGCSE PHYSICS//0625 4.13 Electromagnetic Effects When a magnet is moved towards a coil the pole of the Electromagnetic Induction: If a wire is passed across a coil and magnet next to each other are the same. magnetic field/changing When the magnet is moved away the poles are opposite magnetic field, a small (opposite poles attract). EMF is induced and can The pole-type (north or south) is controlled by the direction in which the current is induced. be detected by a The direction of the current is given by the right-hand galvanometer. grip rule: The direction of an induced EMF opposes the change causing it. The induced EMF can be increased by: o moving the wire faster o using a stronger magnet The fingers point in the conventional current direction o Increasing length of wire in magnetic field, e.g. and the thumb gives the North Pole. looping the wire through the field several times. The current and EMF direction can be reversed by: 4.14 Applications o moving the wire in the opposite direction In a direct current (d.c) the electrons flow in a singular o turning the magnet round so that the field direction is direction. reversed In an alternating current (a.c) the direction of flow is Fleming’s right-hand rule gives the current direction: reversed in regular time periods. A.C Generator: o The coil is made of insulated copper wire and is rotated by turning the shaft; the slip rings are fixed to the coil and rotate with it. o The brushes are 2 contacts which rub against the slip rings and keep the Bar magnet pushed into coil coil connected to the outside part of the circuit, usually made of carbon. o When the coil is rotated, it cuts magnetic field lines, so an EMF is generated, which makes a current flow. o Each side of the coil travels upwards then downwards then upwards etc. so the current flows backwards then forwards then backwards etc. so it is an The induced EMF (and current) can be increased by: alternating current. o moving the magnet faster o using a stronger magnet o increasing the number of turns in the coil If the magnet is pulled away, the direction of the induced EMF (and current) is reversed Using South pole instead of North pole reverses direction of induced EMF (and current) If the magnet is held still, there is no EMF An induced current always flows in a direction such that it opposes the change which produced it. PAGE 18 OF 21  CIE IGCSE PHYSICS//0625 The current is maximum when the coil is horizontal 4.17 Electromagnetic Effect of a Current since field lines are being cut at the fastest rate and 0 Magnetic field around a Magnetic field around a when the coil is vertical, since it is cutting NO field current carrying wire current carrying solenoid lines. The EMF can be increased by: o increasing the number of turns on the coil o increasing the area of the coil o using a stronger magnet o rotating the coil faster 4.15 Transformers Increasing the strength of the field AC currents can be increased or decreased by using a Increasing the current increases the strength of the field transformer. Increasing the number of turns of a coil increases the Consists of a primary coil, a secondary coil and an iron strength increases the strength of the field. core. Reversing the current direction reverses the magnetic The iron core gets magnetized by the incoming current field direction (right-hand rule). and this magnetism then creates a current in the leaving The direction of a magnetic field line at a point is the wire. direction of the force on the N pole of a magnet at that The power is the same on both sides (assume= 100% point efficiency). Magnetic effect of current is used in a relay and a circuit You can figure out number of coils and the voltage with: 𝑶𝒖𝒕𝒑𝒖𝒕 𝒗𝒐𝒍𝒕𝒂𝒈𝒆 𝑻𝒖𝒓𝒏𝒔 𝒐𝒏 𝒐𝒖𝒕𝒑𝒖𝒕 𝒄𝒐𝒊𝒍 breaker. = 𝑰𝒏𝒑𝒖𝒕 𝒗𝒐𝒍𝒕𝒂𝒈𝒆 𝑻𝒖𝒓𝒏𝒔 𝒐𝒏 𝒊𝒏𝒑𝒖𝒕 𝒄𝒐𝒊𝒍 𝑽𝑷 𝑵𝑷 4.18 Force on a Current-Carrying Conductor = If a current carrying conductor is in a magnetic field, it 𝑽𝑺 𝑵𝑺 𝑰𝒏𝒑𝒖𝒕 𝒗𝒐𝒍𝒕𝒂𝒈𝒆 × 𝒊𝒏𝒑𝒖𝒕 𝒄𝒖𝒓𝒓𝒆𝒏𝒕 warps the field lines. = 𝒐𝒖𝒕𝒑𝒖𝒕 𝒗𝒐𝒍𝒕𝒂𝒈𝒆 × 𝒐𝒖𝒕𝒑𝒖𝒕 𝒄𝒖𝒓𝒓𝒆𝒏𝒕 The field lines from the magnet want to straighten out 𝑽𝑷 × 𝑰𝑷 = 𝑽𝑺 × 𝑰𝑺 naturally. (Under 100% efficiency) This causes a catapult like action on the wire creating a When magnetic field is force changed across the primary coil by connecting it with A.C. an e.m.f. induces across the secondary coil. The iron core channels the alternating field through the secondary coil, inducing an alternating e.m.f. across it. A step-up transformer increases the voltage and a step- down transformer decreases it. If you reverse current, you will reverse direction of force Transformers used to make high voltage AC currents. If you reverse direction of field, you will reverse direction Since power lost in a resistor 𝑷 = 𝑰𝟐 × 𝑹, having a of force. lower current will decrease the power loss. Since transmission cables are many kilometres long they have a lot of resistance, so a transformer is used to increase the voltage and decrease the current to decease power lost. The advantages of high-voltage transmission: o Less power lost o Thinner, light, and cheaper cables can be used since current is reduced PAGE 19 OF 21  CIE IGCSE PHYSICS//0625 The direction of the force, current or magnetic field is given by Fleming’s left-hand rule: TURNING EFFECT REVERSING ROTATION CAN INCREASED BY: BE DONE BY: Increasing the current Reversing the battery Using a stronger magnet Reversing the poles o Increasing the strength of the magnetic field Increasing the number of turns on the coil. 5. ATOMIC PHYSICS 5.1 The Atom Atoms consist of: o Nucleus: central part of atom made of protons (positively charged) and neutrons. These two types of particles are called nucleons. They are bound together by the strong nuclear force. 4.19 D.C. Motor o Electrons: almost mass-less particles which orbit nucleus in shells This is proved by Rutherford’s Gold Foil Experiment2 Proton number: number of protons in an atom Nucleon number: the number of nucleons (protons + neutrons) in an atom The following is the nuclide notation for atoms When a current-carrying coil is in a magnetic field, it experiences a turning effect. Isotope: A DC motor runs on a direct current. o Atoms of the same element that have different The coil is made of insulated copper wire and is free to numbers of neutrons e.g. Carbon 12 and Carbon 14. rotate between the poles of the magnet. o There are non-radioactive isotopes and radio- The commutator (split-ring) is fixed to the coil and isotopes. rotates with it. o Radio isotopes are unstable atoms, which break down giving radiation When the coil overshoots the vertical, the commutator changes direction of the current through it, so the forces Uses: change direction and keep the coil turning. o Medical use: cancer treatment (radiotherapy) – rays kill cancer cells using cobalt-60 The brushes are two contacts which rub against the o Industrial use: to check for leaks – radioisotopes commutator and keep the coil connected to battery, (tracers) added to oil/gas. At leaks radiation is usually made of carbon detected using a Geiger counter. The max. turning effect is when the coil is horizontal. o Archaeological use: carbon 14 – used for carbon There is no force when the coil is vertical but it always dating overshoots this position 2 See 20.7 PAGE 20 OF 21  CIE IGCSE PHYSICS//0625 5.2 Detection of Radioactivity Gamma emission: Background radiation: small amount of radiation around Gamma emission by itself causes no change in mass us all time because of radioactive materials in the number or atomic number; they just emit energy environment. It mainly comes from natural sources such Some isotopes do not change in mass or atomic number as soil, rocks, air, building materials, food and drink – however they emit energy as their particles rearrange and even space. themselves to become more stable A Geiger-Müller (GM) tube can be used to detects 𝛼, 𝛽 and 𝛾 radiation 5.5 Half Life Half-life of a radioisotope: is the time taken for half the 5.3 Type of Radioactive Emissions nuclei present in any given sample to decay. Radioactive emissions occur randomly over space & time Some nuclei are more stable than others. ALPHA (𝜶) BETA (𝜷) GAMMA (𝜸) Remember to factor background radiation in half-life Helium calculations involving tables and decay curves One high Electro- nucleus (2 NATURE speed magnetic protons and 5.6 Safety Precautions electron radiation 2 electrons) Radioactive material is stored in a lead container CHARGE +2 -1 none Picked up with tongs, not bare hands Stopped by Stopped by Only reduced Kept away from the body and not pointed at people PENETRATION paper aluminum by lead Left out of its container for as short a time as possible EFFECT FROM Very Not FIELDS Deflected deflected deflected 5.7 Rutherford’s Experiment IONIZING Thin gold foil is bombarded with alpha particles, which Very strong Weak Very weak are positively charged. EFFECT SPEED 1⁄ 𝑣 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 9⁄ 𝑣 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 𝑣 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 Most passed straight through, but few were repelled so 10 10 strongly that they were bounced back or deflected at Depending on their charge, they will be affected by large angles. electric and magnetic fields. Rutherford concluded that the atom must be largely empty space, with its positive charge and most of its 5.4 Radioactive Decay mass concentrated in a tiny nucleus. Radioactive decay: A radioisotope (unstable arrangement of neutrons and protons) is altered to make a more stable arrangement. The parent nucleus becomes a daughter nucleus and a particle (decay products). The nucleus changes when undergoing alpha or beta decay Alpha decay: An element with a proton number 2 lower and nucleon number 4 lower, and an alpha particle is made (2p + 2n) e.g. Radium-226 nucleus → Radon-222 + helium-4 nucleus 226 222 4 88Ra → 86Rn + 2He Beta decay: A neutron changes into a proton, an electron and an antineutrino so an element with the same nucleon number but with a proton number 1 higher e.g. e.g. iodine-131 → xenon-131 + antineutrino + beta particle 131 131 0 0 53𝐼 → 54𝑋𝑒 + −1β + 0v PAGE 21 OF 21  C I EIG CS EPH YS IC S/ /0 62 5 WWW. © Copyri ght2019,2017,2015,2014byZ Notes Fi rstedion© 2014,byZ ubai rJunjuni aforthe2014s y llabus Secondedion© 2015,upda tedbyHarisAlif orthe2016s yl labus Thi rdedion© 2017,upda tedbyMai moonaJ unj uniaf ort he2016-18s yll abus Fourthedion© 2019,upda t edbyKr i shTheobaldforthe2019s y ll abus Thisdoc umentc ontai nimag esandex cer ptsoftextfromeduc aonal res ourcesavail abl eont hei n- ternetandpr intedbook s.Ifyouar etheownerofs uchmedia,textorvis ual,u li zedint hi sdoc u- mentanddonotac ceptit sus agethenweur gey out ocontactusandwewoul dimmedi a telyr e- NOT