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AQA Physics – Energy (Physics Paper 1)

Key Terms Equations to Learn

Chemical Energy Stores

Includes fuels and foods. The energy is transferred during chemical reactions

Energy Transfer

Work Done = Force applied x Distance moved (J)/ (N/m) = (N) x (m)

Equation Number 2: W= F s

Kinetic Energy Stores

Describes a moving object

Kinetic Energy

Kinetic energy = ½ x mass x (speed)2

(J) = (0.5) x (kg) x (m/s) 2 Equation Number 10:

Ek = ½ m v2

Gravitational Energy Stores

Describes the energy an object has if it raised above the ground Gravitational

Potential Energy

GPE = mass x gravitational field strength x height (J) = (kg) x (N/kg) x (m)

Equation Number 11: (Δ)Ep = m g (Δ)h

Elastic Potential Energy

Describes the energy stored in a springy object when you stretch or squash it

GPE = weight x change of height (J) = (N) x (m)

Energy Transfer Energy can not be created or destroyed only transformed from one form to another

Hookes Law: Spring Const.

Force on spring = Spring Constant x Extension (N) = (N/m) x (m)

Equation Number 3: F = k e

Internal Store Energy stored in the movement of particles. Combination of kinetic energy & potential energy of moving particles.

Efficiency

Efficiency = useful output ÷ total input (x 100) (%) = (J) ÷ (J) (x 100)

Equation Number 14:

Joules Unit of energy: One joule (1J) of work is done when a force of one Newton (1N) causes a displacement of (1M) 1 Joule – 1 Newton-metre

Efficiency=useful power in÷total power out(x 100) (%) = (W) ÷ (W) (x 100)

Equation Number 15:

Friction A contact force. Work to overcome this is mainly transferred to thermal energy

Power Power = Energy Transferred ÷ Time (W) = (J) ÷ (s)

Equation Number 12+13: P = E ÷ t

Closed System No net change in the energy of a system Equations given on the Equation Sheet

Work Done Another way of describing energy transfer Elastic Potential

Elastic energy = ½ x spring constant x (extension)2

(J) = (0.5) x (N/m) x (m)2 Ee = ½ k e2

Output Energy The energy given out of a device (useful or wasted)

Input Energy The energy supplied to a device Specific Heat

Capacity

Energy = mass x SHC x temperature change (J) = (kg) x (J/kg °C) x ( °C)

ΔE = m c Δϴ

Non-renewable A resource that cannot be replaced after it has been used

renewable Resources that can replenish themselves

Non Renewable Energy Resources Renewable Energy Resources

Fossil Fuel – Oil, coal, gas

Used in industry & transport. Cheap to mine. Pumped out of the ground in pipes. Limited supply & gives of CO2

Solar From Sunlight infinite energy. Panels can be put on houses

Can be costly to manufacture and maintain

Nuclear Fuel Nuclear fission. Small gives of lots of energy but doesn’t give of CO2. Expensive to run and waste is toxic (storage)

Wind Usually placed on hills (in wind farms) potentially infinite

Manufacture and Implementation can be costly and can be an eyesore

Renewable Energy Resources Geothermal

Heat from Earth in volcanic regions used to heat water

Product from ground may contain dangerous elements Biomass / Wood Cheap can be regrown. Carbon neutral (giving off CO2)

Wave / tidal Ideal for island countries (tidal barrage help flooding)

Construction is costly, environmental issues

Hydroelectric Energy harnessed from GPE KE of water. Can create reservoirs

Costly to build, can cause large scale flooding and effect local ecology

Section 3: Key Terms

21 Electric current

The flow of electric charge.

22 Potential difference

The potential difference between two points in an electric circuit is the work done when a coulomb of charge passes between the points. Potential difference causes charge to flow

23 Resistance

Resistance is caused by anything that opposes the flow of electric charge.

24 ChargeAnything charged that is able to move within a circuit. Electrons or ions.

25 SeriesA circuit with only one route for charge to take.

26 ParallelA circuit with only more than one route for charge to take.

Section 2: Equations to learn

Equation Symbol equation Units

15 Charge flow = current x time Q = I x t Charge flow - coulomb (C)Current – amperes (A)Time – seconds (s)

16 Potential difference = current x resistance

V = I x R Potential difference – volts (V)Current – amperes (A)Resistance – ohms (Ω)

17 Power = potential difference x current

P = V x I Power – watt (W)Potential difference – volts (V)Current – amperes (A)

18 Power = current2 x resistance P = I2 x R Power – watt (W)Current – amperes (A)Resistance – ohms (Ω)

19 Energy transferred = power x time E = P x t Energy = joules (J)Power – watt (W)Time – seconds (s)

20 Energy transferred = charge flow x potential difference

E = Q x V Energy = joules (J)Charge flow - coulomb (C)Potential difference – volts (V)

Section 1: Circuit Symbols

Physics 2: Electricity

1

2

3

4

9

10

8

7

6

5

11

12

13

14

Section 6: The Three Core Cable

32 LiveBrown colour. Current flows to the appliance. Potential difference between this and other wires should be 230V.

33 NeutralBlue colour. Current taken away from appliance. Potential difference should be 0V.

34 EarthYellow and green colour. Potential difference of 0V. Carries charge to Earth if live wire touches the metal casing of an appliance.

Section 5: IV Graphs

29 Fixed Resistor (OhmicConductor)Current and potential difference are directly proportional. Resistance is constant.

30 Filament LampResistance of a filament lamp is not constant. As temperature increases, resistance increases. Ions within the lamp vibrate more, increasing collisions with electrons.

31 Diode/ LEDThe current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction.

Section 4: V, I and R in Series and Parallel

Components connected in…

Current Potential Difference

Resistance

27 Series The current is the same at every point in the circuit and in every component.

The total potential difference of the power supply is sharedbetween the components.

The more resistors, the greater the resistance. The total resistance of two components is the sum of theresistance of each component. Rtotal = R1 + R2

28 Parallel The total current through the whole circuit is the sum of the currents through the separate components.

The potential difference across each component is the same.

Adding more resistors in parallel decreases resistance. The total resistance of two resistors is less than the resistance ofthe smallest individual resistor.

Section 7: Mains Electricity

35 AlternatingCurrent

The current regularly changes direction e.g. mains electricity

36 Direct Current

The current flows in one direction only e.g. batteries.

37 Mains Electricity

UK mains is an alternating current of 230V and at a frequency of 50Hz.

38 National GridA series of cables and transformers linking power stations to consumers.

39 Step-up Transformer

Increases the potential difference for transmission across power cables. This reduces the current and therefore less heat is lost from the cables. This makes the National Grid efficient.

40 Step-down Transformer

Reduces the potential difference fromthe cables to 230V for use by consumers.


Calculation Equation Symbol equation

Units

density density = mass ÷ volume r = m ÷ V kg/m3

volume volume = mass ÷ density V = m ÷ r m3

mass mass = density x volume m = V x r kg

energy needed to change state

energy = mass x specific latent heat E = m x L J

mass mass = energy ÷ specific latent heat m = E ÷ L kg

specific latent heat specific latent heat = energy ÷ mass L = E ÷ m J/kg

energy needed to heat up a substance

energy = mass x specific heat capacity x temperature change

E = m x c x Δθ J

massmass =

energy ÷ (specific heat capacity x temp. change)m= E ÷ (c x Δθ) kg

temperature changetemperature change =

energy ÷ (mass x specific heat capacity)Δθ = E ÷ (m x c) °C

specific heat capacityspecific heat capacity = energy ÷ (mass x temperature change)

c = E ÷ (m x Δθ) J/kg°C

Physics 8: Space

Section 5: Measuring density

Physics 3: Particle Theory of Matter

Key Word Definition

changes of state melting, freezing (solidifying), sublimating, evaporating or condensing

condensing turning from a gas to a liquid

density The mass of a material divided by its volume - Units kg/m3.

eureka can a can used to find the volume of water displaced by an irregular object

Evaporating / vaporisation Turning from a liquid to a gas

freezing turning from a liquid to a solid

internal energy the energy stored by the particles that make up a material

melting turning from a solid to a liquid

physical change a change of state that is reversible

solidifying turning from a liquid to a solid

specific heat capacitythe energy needed to increase the temperature of 1 kg of a substance by 1°C. Units J/kg°C.

specific latent heatthe energy needed to change the state of 1 kg of a substance without changing its temperature. Units J/kg.

state solid, liquid or gas

sublimating turning from a solid straight to a gas without melting

Section 4: changes of state

SOLIDS –• Strong forces of attraction between particles. • Particles vibrate around fixed positions.• Can’t be compressed because particles are very close togetherLIQUIDS –• Particles not in fixed positions, they can slip past each other

hence a liquid takes the shape of the bottom of its container.• Can’t be compressed because particles are very close togetherGASES –• Very weak forces between particles• Particles free to move randomly hence spread out to fill container• Can be compressed because there are large spaces between particles

Section 3: States of Matter

To change the state of a substance, you have to supply energy to increase the internal energy of the substance enough that you overcome the forces between particles. Changes of state happen at a constant temperature because the energy goes into breaking the “intermolecular bonds” between particles. The specific latent heat is the amount of energy you must supply to each 1kg of material to change its state.

Energy = mass x specific latent heat

To measure density, you must find the mass of the object using a top-pan balance, and find its volume. For a regular object e.g. a cuboid, measure the length, breadth and height using a ruler (resolution 1mm) or a Vernier caliper (resolution 0.1mm) or micrometer (resolution 0.01mm).

For an irregular (weird shape) object, use displacement: fill a eureka can with water, drop in the object and use a measuring cylinder to measure the volume of water displaced.

Physics 3: Particle Theory of Matter

Section 6: Particle explanation of gas pressure

Section 7: Particle explanation of convection

Test your knowledge

The barrel of a bicycle pump contains 100cm3 of air at a pressure of 100kPa.The pump is sealed and compressed to a volume of 25cm3 . Calculate the new pressure of the gas.

You drop some nail-polish remover on your hand. Explain why it makes your hand feel cold.

The specific latent heat of fusion (melting) of ice is 334 kJ/kg. (a) How much energy would need to be supplied to melt 10kg of ice?

(b) Describe how the temperature of the ice behaves while it melts.

(c) What happens to the energy supplied to the ice?

Particles are in constant random motion and AVERAGE particle kinetic energy depends on temperature. When particles collide with the container walls, they exert a force on the container. Pressure is force divided by area, so all the forces due to collisions of particles against the container walls causes pressure.If you heat up a fixed mass of gas (same number of particles) gas inside a fixed volume container, its particles move faster (greater average kinetic energy) so they exert a larger force and the pressure increases.If you reduce the volume of a gas but keep the temperature the same, the container is smaller so the particles don’t have to travel as far between collisions with the container walls. There are more collisions per second so the force on the container walls increases, and the pressure increases. Another way of explaining this is that the volume of the container is smaller, the area of the inside is smaller too so Force/Area gives a larger answer for pressure.

Pressure x volume = constant

This formula works for a constant mass of gas at a constant temperature. You might see it written as:

Section 8: Particle explanation of evaporation

Gas heats up, particles average kinetic energy increases and particles spread out. This makes the density of the fluid (gas or liquid) less, so hot, less dense fluid rises and cold, more dense fluid sinks.

EXAM TIP:Make it REALLY clear when you are talking about particles and when you are talking about the fluid (gas or liquid) as a whole.The particles do NOT get less dense, the gas does!

Particles close together, cold air is more dense

Particles spread out, hot air is less dense

The particles in a liquid have a range of kinetic energy. The particles with the most energy have enough kinetic energy to leave the surface of the liquid. This means that the AVERAGE kinetic energy of the particles that are still in the liquid decreases. Temperature depends on the average kinetic energy of the particles. This is why sweat cools your skin.

Section 1: Key words and definitions

Physics 4: Atomic Structure Section 2: Structure of the Atom & Isotopes

Section 3: Nuclear Radiation

absorb To take in

activityHow many nuclei decay per second. Units: Bq (becquerel) or counts per

second.

alpha particleA particle made of two protons and two neutrons that has come from

nuclear decay (looks like a helium nucleus)

atomA neutral particle made of a nucleus and electrons. The smallest amount of

an element you can have.

atomic number The number of protons in the nucleus of an atom

background radiation

Radiation that is around us all the time. Comes from: cosmic rays, rocks, radon gas in the atmosphere, food,

medical scans, nuclear power stations, weapons testing

beta particle A fast moving electron that has come from nuclear decay

contamination When a radioactive material gets into the environment.

electronA particle with negative charge (-1) and tiny mass (0.005). Orbits the

nucleus of an atom.emit To give out

fission A large, unstable nucleus splits into two smaller nuclei and releases a few

neutrons. Also releases energy that is used in nuclear power stations.

fusionTwo small nuclei join together to make a larger one and releases energy in

the process. This is the source of energy within stars.

gamma radiationElectromagnetic wave released by an unstable nucleus during nuclear

decay.

half lifeThe length of time it takes for the activity of a sample of radioactive

material to drop to half of its original value.ionising Capable of pulling some electrons off an atom and turning it into an ion.

irradiationWhen something is exposed to nuclear radiation but does not itself become

radioactive.

isotopesAtoms of the same element that have the same number of protons but a

different number of neutrons (hence they have different mass)

mass number The total number of protons plus neutrons in the nucleus of an atom.

neutron A neutral particle in the nucleus, with charge 0 and relative mass of 1

nucleusThe dense, central part of an atom where most of the mass is concentrated.

Contains protons and neutrons.

penetrating Capable of going deep inside a material.

proton A positively charged particle in the nucleus. Relative mass 1, charge +1

Section 4: Half Life & Radioactive Dating

Isotopes are atoms of the same element that have different mass. Isotopes of an element have the same number of protons in the nucleus but different numbers of neutrons.

The nucleus of a radioactive isotope is unstable and may emit radiation. This makes the nucleus more stable. Alpha, beta and gamma radiation come from an unstable nucleus.

Half life is the amount of time it takes for the number of radioactive nuclei or the measured activity to drop to half of its original value. In radioactive dating, the activity of a sample of ancient wood used to make something is compared with an identical sample of modern wood to find out how much the activity has fallen. This tells us how long ago the tree was cut down.

e.g. if there is only 25% of the expected activity, the tree must have been cut down about 11460 years ago

Atoms have a NUCLEUS in the centre containing protons and neutrons, and electrons orbit the nucleus. A neutral atom has the same number of electrons as protons.

Section 6: Uses of radioactive isotopes

Section 5: Nuclear Decay Equations Section 7: Nuclear Fusion & Nuclear Fission

Section 8: Nuclear Power Stations

Alpha decay changes the nucleus – an alpha particle is made of 2 protons and 2 neutrons so when it leaves, the remaining nucleus has 2 fewer protons and 2 fewer neutrons than before. It is now a different element with an atomic number that has dropped by 2 and a mass number that has dropped by 4.

Beta decay changes the nucleus – a beta particle is made when a neutron in the nucleus turns into a proton and spits out an electron. The remaining nucleus has 1 more proton and 1 less neutron than before. It is now a different element with an atomic number that has gone up by 1 but the mass number has not changed.

Gamma decay is easy – the gamma ray carries away excess energy but the number of protons and neutrons in the nucleus does not change.

In nuclear fission, a large unstable nucleus splits up into two or more smaller nuclei and 2 or 3 free neutrons. Energy is released because the free neutrons have kinetic energy. In a chain reaction, these neutrons go on to cause more fission to happen. For a stable chain reaction, you want only one of the neutrons to cause another nucleus to undergo fission.

A nuclear power station uses nuclear fission of uranium or plutonium to generate heat. The heat is used to make steam to turn a turbine connected to a generator just like in a coal-fired power station.Advantages:• Does not release carbon dioxide• Needs very little fuel to produce a lot of

energy• Easy to control by raising or lowering the

control rods (made of boron which is good at absorbing neutrons) to increase or decrease the rate of nuclear fission

Disadvantages:• Expensive to build and to decommission

(shut down at the end of its useful life)• Produces long lasting radioactive waste

that has to be stored safely• Risk of catastrophic accident

In nuclear fusion, two small nuclei join together (fuse) to make a larger nucleus e.g. in a star, hydrogen nuclei fuse to produce helium. This releases energy. It is very difficult to make nuclear fusion happen in a laboratory because it requires extremely high pressures and temperatures (like you get in the core of a star).

Nuclear fission chain reaction

Alpha radiation is used in smoke detectors. The alpha particles ionise the air and allow a small current to pass across the gap between two electrodes. Smoke particles absorb alpha particles and prevent the current. An electronic system detects a drop in current and sets off an alarm.

Beta radiation is used to monitor the thickness of paper in a paper-mill. If too few beta particles are detected, the paper must be absorbing too many because it is too thick and the rollers are pressed together more to make the paper thinner.

Gamma radiation is used as a tracer in industry and in medicine. In industry, if there is a leak in a pipe underground, a radioactive isotope is put through the pipe and a detector called a “GM Tube” is used to measure the amount of radioactivity on the surface. Where the measurement goes up, there must be radioactive material leaking out of the pipe. In medicine, Tc-99m (technetium-99) is used because it has a half life of 6 hours: long enough to do medical tests but short enough that the patient is not radioactive for too long. A “gamma camera” takes pictures of where the tracer is.


Acceleration Rate of change of speed. How rapidly speed is changing.

air resistance A force that opposes motion. Caused by air particles hitting a moving object.

Balanced forces When the resultant force is zero. Forces are equal in size but opposite in direction.

Braking distance The distance travelled after your foot hits the brake pedal and your car stops.

buoyancy An upwards force on an object that is in air or water.

Displacement The distance in a straight line between your starting point and your finish point.

drag a resistive force e.g. on an object travelling through water

elastic collision a collision where both momentum and kinetic energy are conserved.

Elastic deformation When a material stretches & goes back to original length when you take the force off.

Elastic Potential Energy The energy stored in a stretched material.

Force A push or a pull in a particular direction. Units: newtons (N)

friction A resistive force between two surfaces.

Hooke's LawThe extension (stretch) of a spring is directly proportional to the applied force, up to the limit of proportionality.

inelastic collision a collision where momentum is conserved but kinetic energy is not conserved.

kinetic energy The energy a moving object has. (½ x mass) x (speed squared)

moment A turning force.

momentum Momentum is mass multiplied by velocity. In all collisions, momentum is conserved.

reaction force The upwards force from a solid surface, usually balances the force of your weight.

resultant force Total force when you add up the individual forces, taking direction into account.

Scalar a quantity that has size (magnitude) but no direction.

Speed How fast you are travelling. Speed is distance divided by time.

Stopping DistanceThe total distance between when you first see something in the road and your car actually stopping.

Terminal velocity The constant speed of an object when the resultant force is zero

Thinking distancethe distance your car travels between you seeing an object in the road and you managing to stamp your foot on the brake. Related to your reaction time.

thrust A forwards force e.g. from a car engine

Vector a quantity that has a size (magnitude) and a direction.

Velocity Speed in a certain direction e.g. 30m/s north. Displacement divided by time.

Weight A force on an object because of its mass and the gravitational field of the Earth.

Work Done Energy transferred by a force.


Calculation Equation Symbol equation

Units

Acceleration Acceleration = change in velocity ÷ time a = (v-u)/t m/s2

elastic potential energy

elastic potential energy = ½ x force x extension EPE = ½ F e J

Hooke’s Law Force = spring constant x extension F = k e N

kinetic energy Kinetic energy = ½ x mass x speed squared KE = ½ m v2 J

moment Moment = force x perpendicular distance to pivot Moment = F d Nm

Momentum Momentum = mass x velocity p = m v kg m/s

Newton's 2nd law resultant force = mass x acceleration F = m a N

pressure pressure = force ÷ area P = F÷ A Pa or N/m2

Speed Speed = distance ÷ time v = d ÷ t m/s

Stopping distance Stopping distance = thinking distance + braking distance m

velocity velocity = displacement ÷ time v = s ÷ t m/s

velocity (suvat) v2 - u2 = 2 a s

Weight weight = mass x gravitational field strength W = m g N

Work done Work done = force x distance WD = F d N

Physics 5: Forces

Section 3: Vectors & Scalars Section 4: Resultant Force

Scalars only have size.Vectors have size and direction.

scalar vector

Time Force

Distance Displacement

Speed Velocity

Energy Acceleration

Mass Weight

Momentum

Resultant force is the total force acting on an object when you take account of the direction of each force.If the forces are parallel, just add or subtract. If the forces are perpendicular, use Pythagoras. If the forces are at some other angle, draw a scale diagram & complete the parallelogram.

When you describe a vector, always give a direction too e.g. “momentum is 20 kgm/s to the left”

Physics 5: Forces

Section 8: Stopping Distance

Section 7: Motion Graphs

Section 10: Momentum & Collisions (Sometimes it is rocket science!)

Check which kind of graph you have – displacement (distance) or velocity (speed). Look at the y-axis!

On a v-t graph: gradient is acceleration & area under the line is distance

travelled.

Section 5: Newton’s Laws & terminal velocity

1st Law: An object will either remain at rest or keep moving in a straight line with constant speed UNLESS an unbalanced force acts on it.2nd Law: Unbalanced force causes acceleration (F=ma)3rd Law: Every force has an equal and opposite reaction force.Terminal velocity happens because: At first weight is bigger than air resistance so the object accelerates downwards. As the object gets faster, the force of air resistance on it increases. Eventually air resistance is exactly equal and opposite to weight. Resultant force is zero so the object falls with constant speed.

Hooke’s Law is “the extension of a material is directly proportional to the applied force, up to the limit of proportionality”.

Setup the apparatus shown. Measure the initial length of the spring. Add slotted masses one at a time and measure the new length of the stretched spring each time. To find the extension (the “extra length”), subtract the initial length from each of your results.The slotted masses are each 100g, so each weighs 1.0N.Plot a graph of force against extension. The gradient is the spring constant, k.

Moment of a force = F x dDistance and force must be perpendicular. To increase the moment, increase the length of the spanner handle or push with a larger force.

Increased by:speed, drugs,

alcohol, tiredness, distractions (e.g. using mobile phone)

Increased by:speed, worn tyres, icy or wet roads, worn brakes, extra mass in the car (e.g. lots of luggage)

Stopping distance = thinking distance + braking distance Momentum = mass x velocityIt is a vector – give direction

p = mv

Momentum is always conserved so the total momentum before a collision or an explosion is equal to the total momentum afterwards.Elastic collision – kinetic energy is also conserved.

In an explosion, the total momentum before is 0 because the velocity is zero. After, the total forward momentum equals the total backward momentum. In a rocket, hot exhaust gases are expelled backwards so the rocket must get equal and opposite forwards momentum.

For equilibrium (balance):

12 x 20 = 120Nm 8 x F = 120NmF = 120 ÷ 8

= 15N

Weight acts from the centre of mass. If the centre of mass is pushed beyond the pivot, there is a moment that causes the object to topple over.

Section 9: Turning forcesSection 6: Hooke’s Law – F = k e – practical!

We have to assume there’s no friction


Absorbed Taken in by an object.

Amplitude Distance “from rest to crest”. Maximum displacement of the wave.

Crest The highest point of a wave.

Diffraction When waves pass through a gap or past an edge and spread out.

Electromagnetic spectrum A family of waves that all travel at 300,000,000 m/s in empty space

Emitted Given out by an object.

Equilibrium The rest position of the wave, where displacement is zero.

Frequency The number of waves passing a point in one second. Units – Hertz (Hz)

Longitudinal A wave where the oscillation or displacement is parallel with the velocity

Oscillation A regular movement that repeats over and over

Oscilloscope An electronic device that can be used to study waves

Period The time for one wave to pass a point.

RefractionWhen waves pass across a boundary between two materials and their velocity changes. Makes the waves change direction.

Transverse A wave where oscillation or displacement is perpendicular to velocity

Trough The lowest point of the wave

Ultrasound A sound wave with frequency higher than 20,000 Hz

Wavelength The exact distance from one crest to the next crest


Calculation Equation Symbol equation Units

Wave speed or velocity Velocity = frequency x wavelength V = f x l m/s

Wavelength Wavelength = velocity ÷ frequency l = v ÷ f m

Frequency Frequency = velocity ÷ wavelength f = v ÷ l Hz

Period Period = 1 ÷ frequency T = 1 / f s

Section 3: Electromagnetic Spectrum

Wave Uses Dangers

Gamma Rays Sterilising surgical instruments, sterilising fruit, medical imaging, radiotherapy

Ionising –can cause cancer

X-Rays Looking at shadow pictures of bones and teeth, security scanning luggage at airports

Ionising –can cause cancer

Ultra Violet (UV) In sunbeds for tanning, security marking Skin cancer, sunburn

Visible To see, to take photographs Blindness

Infra Red Cooking food, thermal imaging cameras, TV remote control, fibre optic communication

Burns

Microwaves Cooking food, communicating with satellites, mobile phone communication, “RADAR” speed-guns

Burns

Radio Waves Carrying radio and TV signals None known

Physics 6: Waves

Refraction total internal reflectionSection 4: Ultrasound

Medical uses Industrial Uses

Pre-natal scanningBreaking up kidney stonesMeasuring the speed of blood flow

Cleaning delicate mechanismsFinding cracks in solid metal objectsSonar – to find the depth of the ocean

Radar can tell you how far away an object is. A radar device emits a wave and listens for any echo. If there is an object in the path of the wave, it will reflect some of the wave back to the radar device. EM waves move through the air the speed of light, so the radar device can calculate how far away the object is based on how long it takes the signal to return. Radar can measure the speed of an object, due to Doppler shift. EM waves have a certain wavelength. When the radar gun and the car are both standing still, the echo will have the same wavelength as the original signal. When the car is moving away from the radar gun, the wave gets “stretched out” increasing its wavelength. If the car is moving toward the radar gun, the wavelength decreases.

Ultrasound scans do not damage living cells (like x-rays do) and they produce images of soft tissue (which x-rays don’t). Ultrasound is sent into the patient's body. Some ultrasound is reflected at each boundary between different tissues or organs. The depth of each layer is calculated using the time taken for each reflected wave to return. The reflected waves are processed by a computer to produce a picture of the inside of the body.

Section 5: Lenses and Describing Images

Focal pointSometimes called “principal focus”. The point where parallel incoming rays cross after passing through a lens.

Focal length The distance from the centre of the lens to the focal point

magnification Magnification = image size ÷ object size

Real Image formed where actual light rays cross. Image can be shown on a screen.

Virtual Image is NOT made by actual light rays that cross over. Cannot show image on a screen.

Magnified Image is larger than object

Diminished Image is smaller than object

Upright The right way up

Inverted Upside down

Physics 6: Waves

Section 6: Seeing Colour

Dispersion

A prism will separate out all the colours that make up white light because each colour has a different wavelength and the wavelength affects how much light is refracted through the prism. Red light has longest wavelength and refracts the least. Violet light has the shortest wavelength and refracts the most.

Spectrum What you see when white light gets split up into wavelength order (colours ROYGBIV)

Absorbed If a wavelength (colour) of light is absorbed, it is removed from the spectrum.

Reflected “Bounces off” (do not say bounces off in the exam!)

Transmitted Allowed to pass through

Filter A material that allows only some wavelengths of light to pass through and absorbs all others

Primary colours RED GREEN BLUE – you can’t make these by mixing other colours of LIGHT. (Ignore paint mixing!)

Secondary colours GREEN + BLUE = CYAN; RED + BLUE = MAGENTA; RED + GREEN = YELLOW

Section 1: Permanent Magnets & Electromagnets

Physics 7: Magnetism & electromagnetism

Key term Definition

Permanent magnet A magnet that is magnetic all the time, e.g. a bar magnet or a horseshoe magnet or a fridge magnet

Electromagnet A magnet that can be turned on and off. Needs an electric current in a coil (called a solenoid) to work

Magnetic field An area around a magnet where a magnetic material will be attracted

Magnetic field lines These show the shape of a magnetic field. You can show magnetic field lines with iron filings.

Magnetic material A material that is attracted to a magnet: iron, steel, cobalt & nickel

Section 3: Uses of electromagnets

Electric bell: When you push the switch, the current flows in the coil of wire, the electromagnet turns on and attracts the iron armature. The hammer hits the gong and the contact switch opens. This stops the current and the electromagnet turns off. The iron armature springs back and the whole process repeats.

Relay switch: A small current in the coil turns it into an electromagnet. The iron armature is attracted to the electromagnet and pivots to push the switch contacts closed. This turns on a separate circuit that can have a much larger current. Used in electronic devices and car ignition circuits.

Loudspeaker: Uses the motor effect.An alternating current in the coil of wire makes it into an electromagnet. The electromagnet is attracted and repelled by the circular permanent magnet. The coil is free to move so it vibrates and makes the cone vibrate with the same frequency as the alternating current.

Section 2: Magnetic Fields

Scrapyard electromagnet:Electromagnets can be made much stronger than permanent magnets and they can be switched on and off. In a scrapyard, an electromagnet picks up scrap metals that contain iron or steel and does not pick up any other metals.

We can show magnetic fields by placing paper over a magnet and sprinkling iron filings on it. Tap the paper to show the magnetic field lines.

The magnetic field around a straight wire is concentric circles. The magnetic field of a solenoid (electromagnet) looks the same as around a permanent bar magnet.

Section 4: The Motor Effect

The Motor Effect & Fleming’s Left Hand Rule:A wire with a current in it put in a magnetic field will experience a force because the magnetic field around the wire is repelled by the magnetic field of the permanent magnet. Fleming’s LH rule tells you the direction of the force. You can increase the force by:→ increasing the current→ using a stronger magnet→ coiling the wire into loops

Physics 7: Magnetism & electromagnetismSection 5: Electromagnetic Induction (Generating Electricity)Section 4: The Motor Effect – in more detail

Section 6: TransformersDC Motor: uses this effect. The split ring commutator keeps the current in the correct direction around the loop. You can speed it up by using a stronger magnet, increasing the current, or having more loops of wire on the coil.

Practical motors have many sets of coils at different angles to make their rotation smoother

The Generator Effect: If you move a wire across magnetic field lines, a voltage is induced. To get a bigger voltage: use a stronger magnet, loop the wire into a coil, move it faster.AC Generator / Dynamo: When you make a coil spin in a magnetic field, the wire cuts across the magnetic field lines. A potential difference (p.d. / voltage) is induced. If the coil is connected to a complete circuit, a current is induced too. The p.d. (and therefore the current) is alternating. Slip rings and brush contacts stop the wires from tangling up.To increase the voltage:→ Use a stronger magnet→ Wind more loops(turns) of wire on the coil→ Spin it fasterThe generator in a power station uses electromagnets instead of permanent magnets, and has many more coils of wire.

Transformers change the size of alternating voltages. They are used in the National Grid. A step-up transformer increases the voltage and decreases the current so that less energy is wasted by heating the power lines. A step-down transformer reduces the voltage to a safe level for us to use at home.

Whatever happens to the number of turns, the same happens to the voltage. If the secondary coil has twice as many turns as the primary coil, the output (secondary) voltage will be twice the input (primary) voltage.• An alternating current in the primary coil • makes an alternating magnetic field in the iron core• The magnetic field is moving and cuts across the secondary coil• This induces a voltage in the secondary coil• The induced secondary (output) voltage is at the same frequency as

the primary (input) voltage

A step up transformer has more turns on the secondary coil than on the primary. A step down transformer has fewer turns on the secondary than the primary. The iron core is laminated (made of layers) to reduce energy loss.

Power = current x voltage (P = IV)The power at the secondary coil has to be the same as the power at the primary coil (assuming the transformer is 100% efficient). This means that if the voltage increases, the current must decrease by the same factor – e.g. if the voltage doubles, the current is halved.In reality, the secondary current will be a bit less than we calculate because transformers are not 100% efficient and lose energy as heat.

microphone: Uses the generator effect. • A sound wave makes the diaphragm vibrate. • This pushes on the coil and moves it forwards and backwards over

the permanent magnet. • This movement between the coil and the magnet induces an

alternating current in the wire…• …that has the same frequency as the sound wave.


Artificial satellite A satellite that we have put into orbit to do a job, e.g. GPS satellites

Asteroid A rock orbiting the Sun – most are between Mars and Jupiter

Big bang The most likely theory of how the universe began

Black dwarfThe remains of a small mass star that has become a white dwarf then cooled

Black hole The remains of a very large mass star that has exploded in a supernova

Comet A ball of ice that has a very elliptical orbit with the Sun at one focus

Doppler effectSound waves are squashed up in front of a moving source and stretched out behind it and we hear a change in pitch as it passes us (e.g. an ambulance siren)

Geostationary orbitA satellite orbit where the satellite completes one orbit in 24 hours, so it looks as if the satellite is in the same place in the sky. Used for transmitting satellite TV signals.

Gravitational field Any place where an object with mass feels a force – its weight.

Gravitational field strengthThe amount of weight that a 1kg mass has because of the gravitational field. Symbol “g”. On Earth, g = 9.8 N/kg but we often round to 10N/kg

Natural satellite A natural object that orbits a planet, e.g. our Moon

Nebula A cloud of dust and gas in space – mostly hydrogen

Neutron starA very dense object that remains after a star with a large mass explodes in a supernova

Nuclear fusionThe source of energy inside a star. When two small nuclei join together to make a larger one. E.g. hydrogen nuclei fuse to make helium

Polar orbitA satellite orbit that passes over the north and south poles. Used for satellites that survey the Earth e.g. for weather forecasting.

ProtostarA ball of hydrogen gas that is pulled together by gravity but has not yet started nuclear fusion.

Red giantA small mass star that has run out of hydrogen and has expanded and cooled. Our Sun will become a red giant in about 5 billion years.

Red shiftLight waves are stretched out behind a moving source (e.g. a distant galaxy) and are “shifted” to longer wavelengths.

Red supergiant A large mass star that has run out of hydrogen, expanded and cooled.

Satellite An object that is orbiting a planet

SupernovaThe stage in the life cycle of a very large mass star where it explodes. The outer layers are thrown off and the core collapses into a neutron star or a black hole.

Weight The force on an object because of a gravitational field acting on its mass.

White dwarfThe stage in the life cycle of a small mass star when a red giant cools and shrinks.


Calculation Equation Symbol equation Units

Weight weight = mass x gravitational field strength W = m x g N

mass mass = weight ÷ gravitational field strength m = W ÷ g kg

Gravitational field strength Gravitational field strength = weight ÷ mass g = W ÷ m N/kg

Physics 8: Space

Section 3: The Solar System

The Solar System consists of: • one star (The Sun) at the centre,• Four small, rocky planets –

Mercury, Venus, Earth Mars, • The Asteroid Belt,• Four gas giant planets – Jupiter,

Saturn, Uranus, Neptune• Several dwarf planets e.g. Pluto• Comets• Some of the planets have moons

We have studied the Solar System by: naked eye (i.e. just looking at the night sky), using telescopes on the ground, using telescopes in space (e.g. the Hubble Space Telescope), sending out probes to look closer at distant planets (e.g. Cassini mission studied Saturn in 2017, Voyager 1 & 2 launched in the early 1970s sent back detailed photographs of the gas giants in the 1980s and 1990s), and by sending robotic craft to Mars. (Did you know that Mars is, as far as we know, the only planet entirely inhabited by robots? How cool is that!)

Section 4: Satellites

There are two satellite orbits you need to know about: (The International Space Station is in a low earth orbit)

(1) Polar orbits – satellites in a polar orbit are in a “low earth” orbit that passes over the north pole and the south pole while the Earth rotates underneath. They are fast moving, orbiting the Earth in as little as 90 minutes. This means they can cover the entire surface of the Earth in a day. Polar orbits are used for weather forecasting, analysing land use, anything that involved studying the Earth’s surface.

(2) Geostationary orbits are high above the equator: 36,000km up! A satellite in geostationary orbit completes one orbit in 24 hours.As the Earth also rotates once in 24 hours, it looks as if the satellite stays above the same point on the equator all the time.Communications satellites (e.g. for satellite TV) are in geostationary orbits so that you can point your satellite dish at the same part of the sky and the satellite will always be there.

The further away a satellite is from the Earth, the slower its speed. The closer it is, the faster it goes.

Physics 8: Space

Section 6: The Big Bang

The “Big Bang” says that the universe began about 14 billion years ago as a single point and has been expanding ever since. It is still expanding today. Evidence for the Big Bang includes:(1) Red shift – wherever we look in the universe, light from distant galaxies shows a red shift.

This means that all galaxies are moving away from us, and from each other. The further away a distant galaxy is, the bigger its red shift is. This means that more distant galaxies are moving away faster than closer galaxies. We can use the red shift to tell us two things: the distance away a galaxy is and the speed of a galaxy.

(2) CMBR – Cosmic Microwave Background Radiation. Everywhere we look in space, we see microwave radiation left over from the Big Bang. Originally this was gamma rays but as space has stretched, the waves got stretched too and now they have much longer wavelength than they had when they were formed.

Section 7: Scientific Process (Or – what makes scientists decide which theory is correct?)

Scientists rely on evidence to support their theories. When new evidence is found, it will either support the theory or not. If new evidence does not support the theory, then scientists must modify the theory.Example: Astronomers once thought that the universe had always existed in a “steady state” - its present form. But when evidence of red shift was published, “steady state” theory was replaced by the “Big Bang” theory that the universe began as a single point and is expanding, because there was more evidence to suggest that the Big Bang is likely to be correct. If more new evidence is discovered in the future, even Big Bang theory might have to change!

Section 5: The Life Cycle of Stars

Nebula –

cloud of

hydrogen

Protostar –

gravity pulls the

hydrogen

together

Main sequence star

stable because the

forces are balanced

(weight & radiation

pressure)

Red giant –

SMALL MASS

star runs out of

hydrogen &

swells up

Red supergiant –

a LARGE MASS

star swells and

cools

Black dwarf

– white

dwarf cools

down

White dwarf –

core of red

giant shrinks

and cools

supernova –

a red

supergiant

explodes

Neutron

star

OR

black hole

Our Sun is a small mass star. It will expand to form a red giant, then shrink and cool to form a white dwarf. The white dwarf will cool further to form a black dwarf. Once it is a black dwarf it is at the same temperature as space. Much larger star swell to form a red supergiant, which explodes in a supernova/ The outer layers are thrown off into space but the core collapses to form a neutron star or, if the mass is high enough, a black hole.All elements up to iron were formed by nuclear fusion inside a main sequence star. All elements more massive than iron were formed in a supernova. The atoms in your body were made inside a star. How cool is that (again)!

Test your knowledge

What stages will the Sun go through during the next 5 billion years?

What will happen to a star much more massive than the Sun once it reaches the end of its main sequence stage?

Describe the orbit of a satellite designed to survey the Earth’s surface.

Describe a geostationary orbit and give one use of geostationary satellites.

Outline the current theory of how the universe formed.

What evidence is there to support this theory?

What might persuade scientists to change their mind about a theory?

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