4437 Revision Summary IGCSE Physics

8/12/2019 4437 Revision Summary IGCSE Physics

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IGCSE 44437 Double Award Science: Physics Page 1 of 12

1.2 Understand and use distance-time graphsA horizontal (flat) line means that thedistance is not changing with time.In other words, it is not moving.

By definition, speed = distance / timeso the steepness (or gradient) of theline will give us the speed!Yellow: speed = distance / time = 30 m/ 10 s = 3 m/sBlue: speed = distance / time = 20 m /20 s = 1 m/s

P1.3

P1.4

P1.5 Interpret velocity-time graphsAlways read the labels as the graph looks similar to adistance-time graph.Read as the timeincreases, the speeddoes notchangeThis graph means that the speed is not changing!

As the time increases, the speed increases.This graph shows acceleration.

P1.6


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Shadedrectangle = 20 10 = 200 m

White triangle = (20 20) / 2 = 200 m

Total distance = 200 + 200 = 400 m

P1.7 Express a force as a push or pull of one body on another

P1.8 Identify various types of forceGravitational- attractive force that pulls objects with massElectrostatic- force that acts of 2 (or more) charged objectsOpposite charges attract (positive-negative), like charges repel (positive-positive,negative-negative)Weight acts on a body close to earth

P1.9 Friction is a force that acts in the opposite direction to motionAir resistance acts on bodies moving through airWater resistance acts on bodies moving through waterReaction acts on bodies touching a surfaceTension acts on stretched objects, like stretched springs

P1.10 (unbalanced) Force = mass x accelerationF = m x a

P1.11 Weight = mass x gravityW = m x g

P1.12

Forces acting on a falling bodyWeight always acting down (never changes while the object is falling)Air resistance always acting up (in opposite direction to direction of movement)Air resistance increases as object gets fasterObject accelerates as air resistance is smaller than weightAccelerationspeed increases air resistance increasesTerminal velocity when speed has increased so air resistance now matches weight


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P1.13

Stopping The time takento stop something is called the stopping time. This is made upfrom the thinking and braking times.Thinking You must first decide whether to stop - the process of thinking takes time. We

often call it the reaction time.Braking When the brakes are applied, the car slows down (decelerates). This also takestime: we call it the braking time.Stopping times are not actually that useful to us - we are normally more concerned aboutthe stopping distance. Just as with times, the stopping distance is the total of two parts:Thinking Distance Whilst you are reacting to the hazard, the car is still moving! Duringyour thinking time, you are not slowing down. We call the distance moved during this timethe thinking distance.

Factor Result

TirednessYour brain thinks slower - you will not be able to apply the

brakes as quickly.

AlcoholBeing under the influence - even legally - seriously altershow well you can judge hazards. Your body also movesless accurately. Late or missed braking results!

DrugsMost drugs make you less alert and less aware ofhazards. Even legal pain-killers and hay-fever tablets canseriously affect reaction times.

DistractionsIn-car distractions (e.g. very loud music, mobile phones,crying babies, etc.) take your mind off the road ahead.

Braking Distance With the brakes applied, the car slows down. The distance that the carmoves whilst braking is called the braking distance.

Factor Result

BrakesWorn brakes won't work as well, so you'll need to brake for longer.Modern brakes are also better than old ones - they can apply biggerforces without causing skidding.

Tyres

Not all tyres are the same! Some are designed to reduce fuelconsumption by rolling more easily. This is at the expense of grip inthe wet. Tread patterns are designed to push water out from betweenthe tyre and road. Good tyres can reduce braking distance by manymetres! Worn tyres (with little tread) will have good grip in the dry butin the wet will lead to much longer braking distances...

Road Surface

Different types of surface provide different levels of grip, especially inthe wet. If the road is wet, braking distance will always be longer. Oilspills on the road, gravel, etc. all reduce grip and increase brakingdistances.

MassThe larger the total mass of the vehicle, passengers and luggage, themore kinetic energy it will have at a given speed. This increases thebraking distance as it is harder to slow down.

AerodynamicsRather oddly, the worse your car's aerodynamics, the better it will beat slowing down during braking! The reason is that the airflow at andaround the car (drag or air resistance) is an additional force acting toslow you.


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P1.14

P1.15

See the document Ive sent you on finding the centre of mass of a thin card

On diagrams always draw the weight arrow through the centre of gravityP1.16 Helical springs obey Hookes Law over a large range of extensions

Metal wires obey Hookes LawRubber bands do not obey Hookes Law at large extensions

P1.17

The straight part of a force extension graphobeys Hookes Law. When the graph begins tobend, Hookes Law is broken.


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P2.2 Common electrical conductors Common electrical insulators

Metals Plastic

water Air

P2.3 Hazards of electricity

Long cables- trip hazard Frayed cables- electrocution

Damaged plugs electrocutionMetal objects into sockets- electrocution

Water around sockets/wet hands electrocution

P2.4 Insulation.(a) Cableshave a flexible plastic outer sleeveand the wires inside also have their ownflexible plastic sleeves. These sleeves act as insulation layerswhich stop the coppercore of the live wire from contacting the other wires, any metal part, or the skin of anybodythat is touches the wire.(b) Plug casingsare made of plastic or rubber. Molded plugsattached at the factory aremolded to the cable and are even safer than the plugs that you can take apart.

(c) Double insulationrefers to an appliance that not only has insulated

wires inside, but also has a casing made of plastic, so the potential live partscan't be touched.

Earthing . Appliances with metal cases or other metalparts that might easily be touched are earthed. Thismeans that there will be an earth wireconnecting themetal case to the ground outside via the same electriccables that contain the live and neutral wires. Werethe metal case to become live due to, for example, aloose live wire in contact with it, the current will flowdirectly to earth via the earth wire rather than via theperson who is touching the casing, because the wirehas much lower resistance that the human body andso takes virtually all the current. The earth wire in thissituation acts as a short-circuit.Fusesand circui t beakersThe main job of fuses and circuit breakers is to prevent electrical fires.(a) Fusesconsist of an outer cartridge containing a fine wire. They are 'weak points'deliberately inserted into an electrical circuit. They get hot and melt if the current gets toobig: the fuse is said to blow. Fuses are placed at the live side of appliances and they blow

when there is a sudden big current flowing to earth.(b) Miniature circuit breakersdo the same job as fuses. They are easier to use but costlierthan fuses. They trip(i.e. the contacts separate) when there is too much current and canbe easily resetby pressing a button on the outside of the circuit breaker. When a fusemelts or a circuit breaker trips, the circuit is brokenand the current stops.A Residual Current Device(RCD) is a very sensitive type of circuit breaker. It trips onmuch lower currents than do ordinary circuit breakers and so act as an extra safety deviceif you are using an outside appliance such as an electric lawnmower, hedge trimmer orchain saw. (When you're standing on the grass, current due to an electrical fault will passthrough you to the damp ground more easily than if you were inside standing on carpetfloorboards, since earth is a better conductor.)

P2.5 Electrical heating is used in a wide variety of domestic contexts (in the home).Kettles, heaters, hair-driers, toasters etc.

P2.6 Current in a resistor transfers electrical energy to heat energy. When a resistor gains heatenergy its temperature increases. (It gets hot!)

P2.7 Power = current x voltage P = I x V

Choosing a fuse Calculate current (I = P / V)


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Choose a fuse that can carry a slightly higher current. Too high and it will not blow safely.

P2.8 Energy = Voltage x current x time NB Time MUST BE IN SECONDS!

E= V x I x t

P2.9 Mains electricity is A.C. Electricity from a cell/battery is D.C.

Current/Voltage changes direction 50 timesevery second.

The current always flows from positive tonegative.

P2.10 Parallel circuits are better in the home as they allow many different appliances to workindependently at the same time. If one appliance broke in a series circuit, the whole circuitwould be broken. Also, each parallel branch of the circuit will get 240V. Each part of aseries circuit only gets a share of the full voltage, e.g. two bulbs in series would each getonly (240V/2 =) 120V each so they would be dimmer.

P2.11 The current in a circuit depends on the resistance of the component parts of the circuit andthe applied voltage of the power supply. A circuit (with the same applied voltage) withmore resistance will have less current flowing through it.

P2.12 Current Voltage graphs!

P2.13 If you increase the resistance of a circuit, the current in the circuit will decrease.

If you decrease the resistance of a circuit, the current in the circuit will increase.P2.14 The resistance of a thermistor decreases asthe temperature increases.

The resistance of an LDR decreases asthe light intensity increases.

2.15 Voltage = current x resistanceV = I x R

2.16 Current is the rate of flow of charge (Q). I = Q/t

2.17 Charge = current x time Q = I x t

2.18 Current in a solid metallic conductor is a flow of negatively charged electrons.


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P2.19 A magnetic field line isalso known as a line of force, showing the presence of a magneticfield. Magnetic field lines start on N poles and end on S poles.

P2.20 An electric current produces a magneticfield around it. The Right hand grip rule.The thumb points in the direction of the

current (positive to negative).The fingers of the right hand curl aroundthe wire. The fingers point in thedirection of the magnetic field (North South).

P2.21 When a current-carrying wire is in a magneticfield, the magnetic fields interact, to attract orrepel, just like permanent bar magnets.When the current changes direction (in aloudspeaker) the magnets are attracted andrepelled, pushing the speaker cone in/out,making vibrations that are heard as sound.In an electric motor the forces are oppositeon each side of the coil, causing the coil torotate.

P2.22 Flemings Left Hand Rule1. Label current (all the way round the circuit.2. Label magnetic field in diagram (N S)3. Use the left hand rule to predict thedirection of the force.

P2.23 The force gets bigger when current is bigger magnetic field is stronger

P2.24 When a conductor moves through amagnetic field

OR a magnetic field changes inside aconducting coil

Voltage is induced in the conductor (coil)The induced voltage increases whenThe speed of the conductor is higher The change in magnetic field is greater

P2.25 Electricity is generated whenMagnet rotates inside a coil of wire OR coil of wire rotates inside a magnetic fieldMore voltage when magnet or coil rotate faster


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P3.2 Longitudinal waves Sound, earthquakes, ultrasoundTransverse waves Water waves, light, EM radiation, waves on ropes

P3.3 Amplitude (A) is the maximum displacement of the particles in a waveFrequency (f) is the number of complete waves in 1 secondWavelength ()is the length of one complete wave

Period (T) is the time for once complete waveP3.4 Waves transfer energy/information without transferring matter.

P3.5 Wavespeed = frequency x wavelength V = f x P3.6 Frequency = 1 / Period f = 1/ TP3.7 You must be able to use P3.5 and P3.6 when dealing with waves including sound waves

and light waves. Take care with units! The speed of sound is approx 330 m/s in air.

P3.8 Light is part of the electromagnetic (EM) spectrumAll parts of the EM spectrum travel at the speed of light and behave like light.

P3.9 Recall the order of the EM spectrum including visible light (ROYGBIV)In decreasing wavelength and increasing frequencyRadioMicrowaveInfra-redROYGBIVUltravioletX-raysGamma rays

P3.10

P3.11


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P3.12 Light waves are transverse waves. They can be reflected and refracted.

P3.13 Angle of incidence = angle of reflection (in a flat mirror) NB NORMAL line!P3.14 Virtual image in plane (flat) mirror.

Virtual image is behind the mirror. It is not real. The virtual image(reflection) is the same distance from the back of the mirror as the

object is away from the mirror. The image appear to be back to front.

P3.15 Experiments to investigate the refraction of light in glass blocks/prisms.P3.16 The refractive index n must be greater than 1, e.g. for water n is

approx 1.33.

P3.17 As with P3.15.

P3.18 Total internal reflection keeps light signals inside fibre optic cables, allowing largeamounts of information to be transmitted quickly over great distances.

P3.19 Critical angle is the angle of incidence causing the angle of refraction to be 90 degrees.

P3.20 Remember n must be greater than 1!This means c must be less than 90 degreese.g. for glass with n = 1.5, c is 41.8 degrees.

P3.21 Sound waves are longitudinal waves that can be reflectedP3.22 Humans can hear sounds in the range of frequencies from 20 Hz to 20,000 Hz (20 kHz)P3.23 Measuring the speed of sound by simple direct method

Stand 50 metres from a large smooth brick wallClap once, (start stopwatch) wait to hear echo, then clap again 9 times.Stop stopwatch when you hear 10th (final) echo.Distance travelled by sound 50m x 2 (reflection) x 10 (claps) = 1000m.Speed of sound = distance / time. Speed of sound approx 330 m/s.


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P4.2 Energy transfers examplesP4.3 Energy cannot be created or destroyed.

P4.4,P4.5

Efficiency must always be less than 1 (100%).The energy not converted to useful forms isusually converted to heat/sound due to friction.

P4.6 Heat (thermal) energy can be transferred by conduction (in solids), convection (in liquidsor gases), or radiation (through a vacuum)

P4.7 Convection in everyday phenomena Fridges cooling elements are at the top ofthe fridge to cool the warm air that rises

Kettles use convection to heat all of the water to an even temperature

P4.8 Insulation used to reduce (heat) energy transfersCurtains, carpets, draught excluders, loft insulationCavity blocks, string vests, hair on arms/legs trap air

P4.9,P4.10

Work done = Force x distanceW = F x d

P4.11 Work done = energy transferred

P4.12 Take care not to forget tosquare the speed whenyou calculate the energy.

P4.13 Conservation of energy means that you can assume that all energy is usefully convertedfrom kinetic energypotential energywork. Of course all of it will not be usefullyconverted, so you can mention energy losses like heat/sound.

P4.14,P4.15

Power is measured in Watts (W) orJoules/second (J/s).1 kiloWatt (1kW) = 1,000 Watts.

P4.16 Almost all energy resources produceelectricity by turning a turbine/generator.

Fossil fuels are burned to heat water to turna turbine.


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P5.2

P5.3 Be able to describe how to determine the density of an irregular solid using a balance anddisplacement (Eureka) can.

P5.4

P5.5 Pressure at any point in a liquid or gas acts equally in all directions

P5.6 Brownian motiondescribes the erratic and irregularmotion of particles, such as pollen grains in water.Brownian motion happens when particles that are freeto move around collide with each other, making themboth bounce off in different directions. Many of thesecollisions occur to create the random paths that theparticles take.As an example, observe the movements of pollengrains in water. If viewed under a microscope, you willsee that they move around in completely random anderratic paths. What is happening is that the muchsmaller, and more numerous, water molecules are constantly bombarding them fromall sides. More water molecules hitting the grain on one side than any other side

produces a resultant forceand the grain is pushed in that direction. This happensmany times so that the grain follows a random path.

P5.7 Molecules of gas in a container move at random and collide with the container walls.They exert a force on the walls. The force acting over the area of the container wallsresults in pressure.

P5.8 Absolute zero is the lowest possible temperature and is equivalent to 273 degrees CP5.9 The Kelvin temperature scale begins at absolute zero

0 K (zero Kelvin) = -273 degrees C.To convert Celcius to Kelvin add 273, e.g. 50 deg C = (50 + 273) 323 KNB Do this for every question about gases!

P5.10 Increasing the temperature of a gas will increase the speed of the molecules in the gas(temperature is related to energy)P5.11 In a sealed container, pressure is proportional to Kelvin temperatureP5.12 For a fixed mass of gas at constant temperature p1 x V1= p2 x V2 (Boyles Law)


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P6.2 Describe what is in an atom eg carbon-12atom has 6 protons, (12-6)=6 neutrons and6 electrons

Oxygen-15 has 8 protons, (15-8)=7neutrons and 8 electrons

P6.3 Atomic (proton) number is the number ofprotons(!) eg carbon 6

Mass (nucleon) number is the number ofprotonsANDneutrons eg carbon-12 is 12

Isotope is an atom of the same element with different number of neutrons, e.g.carbon-12 (6 protons, 6 neutrons) and carbon-13 (6 protons, 7 neutrons)

P6.4 Alpha, beta and gamma radiations come out of unstable atomic nuclei. It is a randomprocess. The radiations are ionising, i.e. they can form ions in the material they travel in.

P6.5 Alpha particles are made of 2 protons and 2 neutrons. Weak penetration.Beta particles are high-speed electrons.Gamma rays are high energy EM radiation. Strongest penetration.They can be distinguished (told apart) by their penetrating power.

P6.6 Alpha emission, mass number falls by 4, atomic number falls by 2.Beta emission, mass number does not change, atomic number increases by 1.Gamma emission, numbers do not change.

P6.7 Writing balanced nuclear equations.Make sure you know the numbers for each type of radiation.Treat each line as a maths equation.

P6.8 Ionising radiations can be detected by the effect they make on photographic film or in aGeiger-Muller tube.

P6.9 Background radiation sources; rocks, building materials, cosmic rays, nuclear weaponstests, food.

P6.10 Activity is the number of particles that are emitted from a radioactive source.It is measured in becquerel (Bq). The activity of a source decreases over time.

P6.11 Half-life is the average time taken for the activity of a sample to decrease to 50% of itsoriginal value. Each isotope has a different half-life.

P6.12 Calculations of half-life. Take care to check your answer!P6.13 Radio(active)-isotopes are used to trace (follow) items or in medicine to trace the path of

chemical in the body. It is also used in radiotherapy to treat cancers and to datearchaeological specimens and rocks.

P6.14 Ionising radiations can cause mutations (cancer) in living organismsRadiation can damage living cells (tissue)Radioactive waste may be active for a very long time and have long-term effects on theenvironment.

P6.15 Geiger-Marsden (Rutherford) alpha-scattering experiment using gold foilMost of the alpha particles passed through the gold foil

Some alphas were deflected, some (very few) alphas bounced back off the foilP6.16 Rutherfords model of the atom is a very small dense positive nucleus at the centre of analmost empty atoms, with electrons orbiting the nucleusAlphas passing straight through Atom is mostly empty spaceAlphas being deflected charged nucleus very smallAlpha bouncing back Positively charged very dense nucleus

P6.17 Uranium-235 (U-235) can be split by fission when hit by a neutronThe process releases energy as kinetic energy of the fission products

P6.18 U-235 induced fission produces 2 (large) daughter nuclei (usually Barium and Krypton)and a small number (2 or 3) neutrons

P6.19 A chain reaction can be started if neutrons produced by the first fission strike other U-235

nucleiP6.20 In a nuclear reactor

Control rods can absorb and stop the neutrons from causing further fissionModerator slows down neutrons so they can be absorbed by U-235

4437 Revision Summary IGCSE Physics

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