Physics FlashcardsJakob Hobbs

Forces

SI units kg - unit of mass

m - unit of length

s - unit of time

m/s - speed or velocity

m/s2 - acceleration

N - force

N/kg - gravitational field strength

Nm - torque

Kgm/s - momentum

Distance - Time graphs

A:Speed = gradient

speed is constant.

B:Speed = zero

C: Speed = increasing

acceleration.

D:Speed = decreasing

deceleration.

Displacement - time graph example

This graph has an negative gradient shows an object which is moving backwards at a constant velocity to its starting point.

Average Speed, Distance and Timeaverage velocity,v = displacement,s ÷ time,t

v = s/t

Accelerationacceleration = change in velocity ÷ time taken

a = (v-u)/t

Units = m/s2

It is a vector.

Velocity - time graphs

Velocity = constant

There is no acceleration.

Velocity = increasing

constant acceleration. (acceleration = gradient)

Velocity = decreasing

Constant deceleration.

Area under a velocity time graph

Area under a velocity time graph represents the distance travelled.

Area of triangle = 1⁄2 × base × height

1⁄2 × 8 × 4 = 16 m.

Area of dark-blue rectangle

8 × 6 = 48 m.

Area under the whole graph

16 + 48 = 64 m

Equations of constant acceleration (suvat)

v = u + at

v2 = u2 + 2as

s = ½(u+v)t

s= ut + ½at2

s = displacement (m)

u = initial velocity (m/s)

v = final velocity (m/s)

a = acceleration (m/s2)

t = time taken (s)

Forces, movement, shape and momentum

Examples of forces acting on a car

Other types of forces:Electrostatic, magnetic, upthrust, gravitational etc. A force = a push or pull. It can change

speed, shape or direction.

Scalars and VectorsScalars - has a size (magnitude) only.

Speed,s

Distance,d

Mass,m

Energy,E

Vectors - has a size and a direction.

Velocity,v

Displacement,s

Weight,w

Acceleration,a

Momentum,p

FORCE

Balanced and Unbalanced forcesUnbalanced - When two forces acting on an object are not equal in size.

Resultant force is the difference between the two forces.

Eg 100N - 60N = 40N

FrictionFriction is a force which occurs when objects slide or rub against each other. It can occur in fluids as well.

It opposes motion!

Newton’s 1st Law and 3rd Law

Newton’s 1st Law:

If there is no resultant force acting on an object, it keeps moving with a constant

velocity. Eg : moon, ice rink, air hockey

Newton’s 3rd Law:

If object A exerts a force on object B, object B exerts a force on object A of the

same size and type but in an opposite direction.

i.e every action has an equal and opposite reaction.

Force, Mass and accelerationAn object will not change its velocity unless there is an unbalanced force.

F = m × a

From this you can see that 1N is the force needed to make a mass of 1kg acceleration at 1m/s2

Newton’s 2nd Law

Weight and MassMass is the measure of the amount of matter in an object.

Weight is the measure of the force of gravity pulling down on an object with a mass.

Weight (N) = mass (kg) × gravitational field strength (N/kg)

W = m × g.f.s

On earth g.f.s = 10N/kg

Stopping distance

Thinking distance + braking distance = stopping distance

Thinking distance - the distance travelled by the car from when the

driver sees the hazard to applying the brakes.

Braking distance - the distance travelled by the car in order to stop

after applying the brakes.

Calculating stopping distanceEg calculate the stopping distance at 30m/s

Thinking distance = reaction time × speed

0.5 × 30 = 15m

Braking distance

v2 = u2 + 2as

0 = 302 + 2 × - 6.67s (deceleration = - 6.67m/s2)

B.D = 67.5m

S.D = 82.5m

Factors affecting thinking distance

● Greater velocity = greater thinking distance.● Use of drugs/alcohol - slower reaction time =

greater thinking distance.● Tiredness - slower reaction time = greater

thinking distance.● Distractions - slower reaction time = greater

thinking distance.

Factors affecting braking distance

● Greater velocity = greater B.D (double velocity×4 braking distance.)

● Surface of road - smoother road = greater B.D ● icy/wet road = greater B.D ● Function of the brakes● Worn tyres = greater B.D● Larger mass = greater B.D

Graph of stopping distance

Effect of velocity on Braking distance InvestigationEquipment = trolley, track, light gate, metre rule, a brake.

Results:

This graph shows positive correlation showing that as velocity increases braking distance increases. They are not directly proportional.If you double the velocity the BD is times 4.

To calculate the speed divide the length of the card strip by the time taken to pass through timing gate.

Movement - Deceleration in a collision Eg// A car travelling at 20m/s hits a wall and stops in 0.02s. Calculate the deceleration.

a = (v-u)/t

a = 20/0.02

= -1000m/s2

Eg// Calculate the force a person of 50kg experiences.

F= m × a

F = 50 × 1000

F = 50000N

Air resistance and Terminal velocityAn object moving through air experiences air resistance or drag.

The size of the drag force depends on size and speed.

A drag coefficient is a measure of how easily an object moves through air.

Streamlined, smooth surfaces produce less drag.

Smaller surface areas produce less drag.

Terminal velocity● The object has weight pulling it

down causing it to accelerate.● However, as it falls drag

opposes motion.● As velocity increases drag

increases and acceleration becomes slower.

● Weight and drag will become balanced and there will be no resultant force.

● There will be a constant velocity.

Practical - terminal velocity1) Measure 10 cm intervals on a tube filled with oil. 2) Measure the diameter of the sphere. 3) Put the sphere in at the time. 4) Measure the time over the distance. 5) Repeat and average. 6) Use velocity = distance/time.7) Determine velocity at different points and plot a graph.

Parachutes

Hooke’s LawThe applied force is directly proportional to the extension as long as the limit of proportionality is not passed - applies to all metals. F ∝ x

Elastic limit - the point beyond which it will not return to its original length after the load has been removed.

Elastic - returns to original shape when load is removed.

Plastic - does not return to original shape when load is removed.

* The greater the spring constant (gradient) the stiffer the spring.

Investigating extension in springs1) Measure length of spring without any weight first.2) Add a weight and measure the length. 3) Subtract the original length from this to get the extension.4) Repeat for a variety of weights. 5) Plot a graph of extension against force.6) If proportional the graph will be a straight line and an extension line will pass through the origin.

Safety: ● Wear eye protection.● Do not use excessively large loads.

Increasing accuracy:● Use a set square ● Ensure that the ruler is held at 90 degrees to the base through using another clamp stand.● Digital calipers.● Ensure the spring has stopped moving before measuring.● Measure from the same part each time.

Graphs of Extension

Elastic bandsDo not obey Hooke’s Law.

Momentummomentum = mass × velocity

p = m × v

Momentum is a vector.

Unit: kgm/s

The sign of momentum tells you the direction. Positive means travelling East and negative means travelling West.

ExampleA 3kg trolley is moving at 2.0m/s East. A 4.2N force acts on it for 6s. Calculate the new momentum.

1) Calculate acceleration:

F =ma 4.2/3.0 = 1.4m/s2

2) Velocity change:

Acceleration x time 1.4 x 6 = 8.4m/s

3) New velocity:

2+8.4 = 10.4

4) New momentum:

Mass x velocity = 3x 10.4 = 31.2kgm/s

Impulse and Momentum

Force = change in momentum/time

Momentum and safety features

Seat Belts, crumple zones etc.

1) Increase the time taken

2) For the same change in momentum

3) Which reduces the force needed

4) Which reduces the chance of injury.

Conservation of momentumIf no external resultant force acts on a system then the vector sum of momentum remains the same i.e momentum is conserved.

Total initial momentum = Total final momentum

Σp1 = Σp2

Σmu = Σmv

Eg: Firing a gunMass of gun = 5kgMass of bullet = 0.012kgInitial velocities = 0The final velocity of the bullet = 400m/s

What is the recoil velocity?

(5 x 0) + (0.012 x 0) = (5 x v) + (0.012 x 400)5v = -4.8kgm/sv = -0.96m/s

Momentum question

Moments

Moment = Force x perpendicular distance from the pivot

It is the ‘turning force’

Moment = F x d

The unit is Nm

Principle of moments

If a system is in equilibrium:

the sum of the clockwise moments = the sum of anticlockwise moments

Centre of gravity

The weight force of a body acts through the centre of gravity.

When an object is not pivoted through the centre of gravity the weight force of the object will produce a turning effect.

Stability

Wider base.

Lower centre of gravity.

A turning moment tries to pull it back to its original position.

Question

As the painter moves towards Plank A the force on it will increase because the plank is balanced meaning that sum of anticlockwise and clockwise moments is the same. This means that at A a greater force will be applied to produce the same moment.

Electricity

UnitsAmpere (A)

Coulomb (C)

Joule (J)

Ohm (𝛀)

Volt (V)

Watt (W)

Circuit symbolsThe longer line of a cell is positive and the shorter line is negative.All electrical circuits are drawn as though the current flows from positive to negative.

Energy and voltage in circuits

Electrical conductors and insulatorsMetals are good conductors - free electrons which can move and carry charge.

Their movement is random but when connected across a conductor the negatively charged electrons flow towards the positive terminal - net flow of charge.

In insulators electrons are held tightly in position and are unable to move from atom to atom so charges are unable to move through insulators.

Complete circuit - charge can travel all the way round.

Incomplete circuit - gaps so charge cannot travel all the way round.

Current● Electrical current is the rate of the flow of charge round the circuit.

● Amps (A) - ammeter in series.

● In series the current is the same everywhere.

● The size of the current depends on the voltage applied to it and the number and type of the other components.

● In parallel current divides at any point where wires divide.

● Current = Charge/Time (I = Q/T)

● In a solid metallic conductor it is a flow of negatively charged electrons.

● Current is conserved at each junction because the number of electrons that flow into a junction each second must be the same as those which leave each second.

● Bulbs and LEDs can be used to detect current.

Voltage● The voltage across a component is the difference in electrical potential energy

between the two sides.

● Voltage is the energy transferred per unit charge passed.

● The volt is a joule per coulomb.

● Voltage is measured in volts, V.

● It is measured with a voltmeter in parallel across the component.

● Voltage = Energy transferred/charge

● V = E/Q

● The potential difference across components in series adds up to the supply.

● The potential difference across components in parallel is the same as the supply.

Series and parallel circuitsSeries:● One switch placed anywhere can turn the circuit off.● If one bulb breaks it causes a gap in the circuit and current no longer flows.● The energy supplied by the cell is shared between the bulbs so the more

bulbs you add the less bright they are.● Less wiring.

Parallel:● Switches can be placed in different parts of the circuit to switch off individual

branches.● If one bulbs breaks only the same branch is affected.● Each branch of the circuit receives the same voltage so if more bulbs are

added to the circuit they keep the same brightness.

Uses of series and parallel circuitsDecorative lights are wired in series.

● Each bulb only needs a low voltage so even when the voltage from the mains supply is shared between them each bulb has enough energy to produce light.

● If one bulb breaks all the other bulbs will go out.

The lights at home are wired in parallel.

● Lights can be switch on and off separately and the brightness of each light does not change.

● If a bulb breaks you can still use the other lights. ● They all receive the same voltage. ● Parallel requires more electrical wire.

ResistanceResistance is anything in the circuit that reduces the current.

It is measured in ohms Ω

Ohm's Law - Voltage = current x resistance

V = IR

Resistors in series - Total resistance = sum of individual resistances RT = R1 + R2

Current flows when electrons move through a conductor. The moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow, and causes resistance.

Wires in toasters have high resistance. As current flows energy is transferred and the element heats up.

Factors affecting resistance

● material e.g. copper has lower resistance than steel

● length - longer wires have greater resistance electrons collide with more ions.

● thickness - thicker wires conduct better as more charge can pass each second.

● temperature - heating a wire increases its resistance because the electrons collide more often with ions as the electrons move faster (as they have more kinetic energy) and the atoms vibrate more.

Practical

1) Turn variable resistor to maximum. 2) Close the switch and take

readings from ammeter and voltmeter.

3) Decrease value of variable resistor and repeat.

4) Plot a graph of current against voltage.

5) Between readings open the switch.

Voltage - Current graphs - wires, resistorsCurrent is directly proportional to potential difference so the resistance of this component does not change. It obeys Ohm's Law.

The 1/gradient is the resistance so the steeper the slope the smaller the resistance.

If the axis are the other way round the gradient is the resistance.

Lamps The lamp doesn’t obey Ohm’s law because it is not a straight line (current is not directly proportional to voltage) indicating that resistance changes.

At higher currents and voltages the slope of the graph becomes less steep indicating that resistance has increased.

This is because as the temperature of the filament increases the current decreases as there is more resistance.

High resistance

Low resistance

Diodes

The diode has a very high resistance in one direction.

This means the current will only flow in one direction so doesn’t obey Ohm’s Law.

High resistance

Low resistance

Using resistance - fixed and variable resistorsFixed resistors are used to control the size of currents and voltage.

Variable resistors make it possible to alter their resistance.

If resistance is decreased it will shine more brightly and if resistance is increased the bulb will shine less brightly.

The variable resistor act as dimmer switch.

It can be used in motors to control its speed.

Thermistors Thermistors change their resistance with temperature.

It is the reverse of the lamp. As more current flows the graph gets steeper. This is because as temperature increases resistance decreases.

Thermistors are used in temperature sensitive circuits in devices such as fire alarms or freezers (to ensure no change in temperatures).

LDRA light dependent resistor has a resistance that changes when light is shone on it.

In dark resistance is high but in light resistance decreases.

LDRs are often used for automatic lighting controls and burglar alarms.

Calculating resistance using graphsThe slope of a voltage - current graph shows resistance.

For straight lines R = 1/gradient.

The steeper the graph the lower the resistance.

InvestigationsBasic Plan

Results

Accuracy

Constant temperature - rate of energy loss = supply.

In graphs - proportional/inverse + linear vs non-linear

LEDs are more efficient than filament lamps because they waste less energy as heat. (efficient = useful/total)

Mains electricity

Mains electricity Ring main circuits usually consist of three wires:

Live: ● Provides the path along which electrical energy travels.

Neutral: ● Completes the circuit.

Earth: ● Safety feature which protects the user if there is a fault.

Fuses● Fuses are deliberate weak links in the circuit. ● A thin piece of wire from a metal with a low melting point. ● If the current increases over the max value of a fuse the wire

becomes hot and melts breaking the circuit. ● This prevents shocks and stops wires in circuit overheating.● Fuses and switches should go on the live wire.

Circuit breakers● They switch off automatically if there is too large a current. ● The switch can be reset and does not need to be replaced. ● They work more quickly and do not require an earth wire.● RCCB detects the change in current during a fault. ● They can work for small current changes.

Residual current circuit breaker.

Labelled plug

Choosing a fuse1) Find the power rating in watts of the appliance. 2) Find the potential difference (230V).3) Calculate the current used I = P/V4) Choose the next biggest fuse. 1A, 3A, 5A, 7A,13A

Earth wires and double insulating1) The earth wire should be connected to the metal casing.2) If the live wire comes into contact the earth wire provides a low resistance

path for the current and the current goes to the earth.3) This means there is a large current in the earth wire. 4) The fuse melts and cuts the circuit. 5) Without the earth wire anyone touching the casing would receive a shock.

Double insulation:

● Casings are made from an insulator such as plastic - no need for earth wire. ● Protects people from shocks.

PowerPower is the rate of transfer of energy or rate of doing work.

Power = Energy transferred/time takenP=E/T

Watt is the unit of power.

Electrical power = current x potential differenceP = VI

Electrical energy = ItV (time in seconds)E = QV

Kilowatt-hour kWh - A unit of energy.

AC vs DC An electric current flows either as a direct current or as an alternating current.Direct current:● A direct current flows in only one direction.● Car batteries, dry cells and solar cells all

provide a direct current.Alternating current:● An alternating current continuously changes

from positive to negative.● In the UK, the mains electrical supply is

generated at a frequency of 50 Hertz (Hz) and is delivered to houses at 230 Volts (V).

An oscilloscope screen displaying the signal from a direct current (DC) supply. It is a horizontal straight line at 1.5V.

Alternating current. It is a curve alternating between positive and negative voltages.

Transmitting electrical energy using high voltages1) High voltage leads to low current.2) P=IV3) Less energy is lost from the wires.4) More efficient.5) Can use thinner wires.

Electric charge

Electrical chargePositive and negative electrostatic charges are produced on materials by the loss and gain of electrons.

Charging materials by frictionThese objects must be made of different materials

To test this use an uncharged cloth and plastic rod.

1) Rub them together.2) Electrons are transferred.3) Electrons have a negative charge and the object becomes negatively charged

gaining electrons or positively charged by losing electrons.4) They must be electrical insulators. 5) We say that charges have been induced.

Forces between chargesSimilar charges repel.

Opposite charges attract.

Electrostatic paint spraying

Droplets have the same charge so repel each other creating a mist resulting in better coverage. Less paint is used.

Inkjet PrintersInkjets direct a fine jet of ink drops onto paper.

Each spot is given a charge so that as it falls between a pair of deflection plates, electrostatic forces direct it to the correct position.

The charges on the plates change hundreds of time each second so that each drop falls in a different position.

Photocopiers1) Drum becomes positively charged.2) The surface is covered in selenium.3) A bright light is shone on the paper. 4) The white parts of the paper to be copied

reflect the light on to the drum and the dark printed parts do not.

5) In those places where light is reflected selenium loses its charge but where there was no reflection of light charge remains.

6) Negatively charged carbon powder called toner is blow across the drum and sticks to charged parts.

7) The paper is pressed against the drum. 8) The powder is fixed by heater.

Electrostatic Precipitators

Problems with static electricityAs aircrafts fly through the air friction causes them to become charged.

After the aircraft lands there is the possibility of charges escaping to earth as a spark.

If this takes place during refuelling there could be an explosion.

The solution is to earth a plane with a conductor as soon as it lands.

Fuel tankers on roads are also earthed before refuelling.

● Metal conductor. ● Current flows in the earth wire.● This discharges the tanker.

IDEA OF WEIGHT IMPORTANT.

Storm clouds1) Electrons move to earth (negatively charged).2) Air conducts. 3) Lightning.

Waves

UnitsHertz (Hz)

Metre (m)

metre/second (m/s)

Second (s)

Degree (°)

Properties of waves

Waves● A wave are vibrations that transfer energy or information from place to place

without transmitting matter.● A wavefront is created by overlapping lots of different waves. It is a line where all

the vibrations are in phase and the the distance from the source.

Transverse wavesTransverse wave:

A wave that vibrates or oscillates at right angles to the direction of energy transfer or velocity.

ffff

The spring is moved from side to side.

Particle oscillation

Longitudinal wavesLongitudinal wave:

A wave in which the vibrations or oscillations are along the direction in which the energy or wave is moving.

The spring is pushed and pulled.

Eg sound

Describing waves Amplitude,A (m) - The maximum movement of an oscillation from its resting or equilibrium position.

Wavelength (m) - The distance between a point on one wave and the same point on the next wave.

peak/crest

trough

Describing waves (2) Frequency,f (Hz) - The number of waves produced each second by a source, or the number passing a particular point each second. (number of oscillations/second).

Time period, T (s) - The time taken for 1 complete oscillation.

Frequency and time period are linked by the equation:

Frequency,f (Hz) = 1/time period, T (s)

f = 1/T

Wave speed equationWave speed,v (m/s) = frequency,f (Hz) × wavelength,𝛌 (m)

v = f × λ

Eg// What is the speed of a water wave that has a frequency of 0.5Hz and a wavelength of 3m?

v = 0.5Hz × 3m

v = 1.5m/s

Investigating water waves

Plane waves at a higher frequency.The wavelength is shorter.

Plane waves at a lower frequency.The wavelength is longer.

Radial waves

This shows radial waves interfering constructively and destructively.

This shows a radial wave. The waves spread out in a circular direction.

Concave and convex obstructions

Diffraction

This shows diffraction through a large gap. The plane waves curve and spread out.

This shows diffraction through a smaller gap. The plane waves curve and spread out.

● When waves meet a gap in a barrier, they carry on through the gap.● The waves spread out into the area beyond the gap. This is diffraction.● The extent of the spreading depends on how the width of the gap

compares to the wavelength of the waves. ● Significant diffraction only happens when the wavelength is of a similar

size as the gap (light is an example).

Refraction

As the waves enter shallow water they slow down and change direction due to refraction.

If the wave enters a denser medium, its speed decreases and it bends towards the normal.

If the wave enters a less dense medium, its speed increases and it bends away from the normal.

ReflectionAll waves can be reflected.

If they hit a straight or flat surface the angle of incidence,i = the angle of reflection,r.

Doppler EffectWhen the ambulance is moving, the wavefronts ahead of the car are compressed.

The waves will have a shorter wavelength and a higher frequency.

Person B hears a sound that has a higher pitch.

Person A hears a lower pitch as the wavefronts are more stretched out so so have a lower frequency.

A B

The electromagnetic spectrum

Electromagnetic spectrumThe electromagnetic spectrum is a continuous spectrum of waves.

At one end the waves have very long wavelengths and low frequencies.

At the other end the waves have very short wavelengths and high frequencies.

1) They all transfer energy.2) They are all transverse waves.3) They all travel at the speed of light in a vacuum (300,000,000m/s)4) They can all be reflected and refracted.

Wave

Radio

Microwaves

Infrared

Visible light

Ultraviolet

X-rays

Gamma-rays

Radio wavesRadio waves have the longest wavelengths and lowest frequencies.

They are usually used for communication and broadcasting. (radios and TV)

Radio waves are emitted by a transmitter and are detected by an aerial.

MicrowavesMicrowaves are used for communications, radar and cooking foods. (Produced by a magnetron!)

Food placed in a microwaves oven cooks more quickly than a normal oven. This is because water molecules in the food absorb the microwaves and become very hot. The food cooks throughout rather than just from the outside.

Microwaves have metal screens that reflect microwaves and keep them inside the oven. Microwaves cause internal heating of human body tissue.

Microwaves 2Mobile phones transmit much less energy than those in a microwave oven.

Microwaves can easily pass through the Earth’s atmosphere and so can carry signals to orbiting satellites.

InfraredAll objects emit Infrared radiation. (detected by blackened thermometer etc.)

Hot objects emit more energy as infrared radiation.

Uses: Infrared cookers and heaters, TV remotes, night vision.

They have low penetrating power so will operate over short distances and are unlikely to interfere with other waves.

They can cause skin burns.

Visible lightUses: photography and optical fibres.

Detected by: the eye, light dependent resistors etc.

Colours of the visible spectrum:

White light can be split up to form a spectrum using a prism.

The light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted. As a result, red light is refracted the least and violet light is refracted the most - causing the coloured light to spread out to form a spectrum. This is called dispersion.

Ultraviolet lightProduced by: the Sun and UV lamps. (detected by: skin, fluorescent chemicals).

Can cause blindness.

UV light causes the skin to tan, but overexposure damages surface cells and can lead to sunburn.

It can also cause skin cancer.

The ozone layer absorbs most of UV radiation but due to pollution the ozone layer is becoming thinner. This may lead to increased numbers of skin cancers.

Some chemicals fluoresce under UV light. This property is used in security marker pens.

Kills bacteria so is used to sterilize equipment.

Fluorescent lamps

X-RaysProduced by: X-Ray machines. (Detected by: photographic film).

Medical uses: X-rays pass easily through soft body tissue but not bones. Therefore pictures can be used to examine a patient’s bones.

Used for cancer treatment (radiotherapy).

Other uses: To check internal structures of objects eg airport security.

It can cause cancer so radiographers stand behind lead screens and wear protective clothing. Distance

Gamma RaysHighly penetrating waves that can cause damage to living cells (cancer).

They are produced by unstable nuclei.

They are used to sterilize medical instruments and to kill microorganisms so that food can keep longer.

It is also used to treat cancer (radiotherapy). Large doses of gamma rays targeted at cancerous growth kills cancer cells completely. They can also cause cancer as they have a really high energy and damage healthy cells. Doctors are exposed for longer time periods.

Distance = protection.

Light and sound

Light Waves - ReflectionWhen a ray of light strikes a plane mirror, it is reflect so that the angle of incidence,i = angle of reflection,r

PeriscopePeriscopes use to mirrors to change the direction of light.

Rays from an object strikes the first mirror at 45° to the normal. The rays are reflected at 45°. At the second mirror the same occurs.

Refraction● As the light enters the block

there is a change of medium● It slows down and bends

towards the normal (i>r). It has a greater refractive index.

● When light leaves a glass block, it accelerates and bends away from the normal.

● At 90° the ray is not refracted.● Wavelength decreases.

Refraction investigation1) Draw around the glass block.2) Mark positions of incident and emergent rays.3) Remove block and draw refracted ray.4) Measure angle of incidence.5) Measure angle of refraction.6) Measure angles to the normal.7) Repeat for a range of value. 8) Plot a graph of sin(i) against sin(r).9) Use the gradient to calculate the refractive

index.

Refractive IndexDifferent materials can bend rays of light by different amounts.

Refractive index =

Glass = 1.5Water = 1.3

It is only a ratio so does not have a unit.

The value is always above 1.

To obtain more accurate values repeat for a range of values and plot a graph of sin(i) against sin(r). Then calculate the gradient. It then relates to all the data and eliminates anomalies.

Partial Internal Reflection

When a ray of small incidence passes from glass to air, most of the light is refracted away from the normal but a small amount is reflected from the boundary.

This is called Partial Internal Reflection. (i<c)

As the angle of incidence increases, the angle of refraction also increases until it reaches the critical angle,c. Angle of refraction = 90°. (i=c)

The critical angle is the smallest possible angle of incidence at which light rays are totally internally reflected.

Total internal reflection

When i>c all the light is reflected at the boundary. No light is refracted. The light is totally internally reflected.

It must be going from optically more dense to less optically dense.Glass has a higher refractive index than air.

Investigating total internal reflection

Critical angle equationFor light passing from glass to air the critical angle is typically 42°.

Critical angle for a particular medium is related to its refractive index in the equation: sin(c) =

Prismatic PeriscopeThe image produced by prisms is often brighter and clearer than those produced by mirrors. Therefore prismatic periscopes are often used.

Light passes through the surface AB of the first prism at 90° and so doesn’t change direction. It the strikes the surface AC of the prism at the angle 45°. The critical angle of glass is 42° so the ray is totally internally refracted. The same happens at the second prism.

Bicycle and car reflectors and binoculars

DiamondsDiamond has a high refractive index.

This means it has a small critical angle.

When the critical angle is passed total internal reflection occurs.

If this is smaller it is more likely to occur as there are less angles of incidence which are under this value.

Optical FibresEndoscope

● Optical fibres bend.● Some fibres carry light to the inside of the patient whilst

others transmit the reflected light inside the patient.● Light passes up/down fibres by TIR. Light entering the

inner core always strikes the boundary at an angle that is greater than the critical angle so is totally internally reflected.

● Large numbers of these fibres fixed together form a bundle. They can carry sufficient light for images to be seen through them.

● If they are narrower at one end they can produce a magnified image.

● On exit it refracts bending away from the normal.

Optical fibres in telecommunication

Modern telecommunications systems use optical fibres rather than copper wires to transmit messages as much less energy is lost - more information per second.

Electrical signals are converted into light energy and are sent in pulses down optical fibres.

A light sensitive detector at the other end changes the pulses back into electrical signals.

Digital and analogue

Communications signals can be analogue or digital.

Analogue signals● Vary continuously in frequency and amplitude.● FM and AM radio - Frequency Modulated radio and Amplitude

Modulated radio. Digital signals

● Digital signals are a series of pulses consisting of just two states: ON (1) or OFF (0).

● They carry more information per second than analogue signals.● They maintain their quality over long distances better than analogue

signals.● To increase the amount of information carried:

○ Increase bit rate.○ Increased bandwidth.

SoundSound waves are produced by objects vibrating.

We hear sounds when these vibrations, travelling as sound waves reach our ears.

Sound waves are longitudinal waves which can be reflected and refracted.

Eg ships use echoes to discover depth of water. - sonar

1) Sound waves are emitted by the ship.2) Some of these are reflected from the seabed back up to the ship.3) The ship detects these.4) The time taken for the waves to make its journey is measured.5) The depth can the be calculated.

Measuring the speed of sound1) Equipment - two bits of wood and a stopwatch.2) Stand 50m away from person with the wood. 3) Bang the two pieces of wood together and start the stopwatch. 4) Stop the stopwatch when you hear the sound.5) Use the s=d/t equation to calculate the speed.6) This will not be very accurate since reaction speed is crucial - high percentage error.7) Repeat and average.Alternatively:1) Stand 50m away from a large wall.2) Bang the two pieces of wood together and listen for the echo.3) Bang the pieces of wood together each time an echo is heard.4) Time yourself doing 20 claps.5) During this time the sound will have travelled 50 x 20 x 2 (since it has gone to the wall

and back 20 times).

Refraction of sound

Pitch and frequencySmaller objects vibrate quickly and produce sound waves with a higher frequency and therefore pitch.

Larger objects vibrate more slowly and produce sound waves with a lower frequency and therefore pitch.

The frequency is the number of complete vibrations each second. (measured in Hz).

The audible frequency range for humans is 20 - 20000 Hz

Investigating the frequency of sound using an oscilloscope

1) Connect a microphone to an oscilloscope.2) Adjust the oscilloscope to get a steady trace.3) Adjust oscilloscope to give a minimum of 1 complete cycle on the screen.4) Measure the number of squares for a number of complete cycles. 5) Multiply number of squares by the time base.6) Find the time period.7) use f = 1/T.

LoudnessThe amplitude of the vibration determines loudness.

Higher amplitudes mean louder sounds.

Lower amplitudes mean quieter sounds.

Energy

UnitsKilogram (kg)

Joule (J)

Metre (m)

metre/second (m/s)

metre/second2 (m/s2)

Newton (N)

Watt (W)

Energy transfers

Energy storesChemical - Energy stored in food, fuel, batteries etc.

Kinetic - Energy stored in moving objects.

Thermal - Energy stored in objects due to their temperature.

Gravitational potential - Energy stored in objects that are raised up.

Elastic potential - Energy stored in objects that are stretched, squashed or twisted.

Magnetic - The energy stored by two separated magnets.

Electrostatic - The energy stored by two separated electric charges.

Nuclear - The energy stored inside atoms’ nuclei. Released in nuclear reactions. (source of the sun’s energy).

Energy TransfersHeating (conduction/convection) - The transfer of thermal energy.

Electrical - The transfer of energy by means of electrons in wires.

Mechanical - This transfer uses forces to transfer energy.

Radiation - The transfer of energy by waves (Eg light and sound).

Conservation of energyEnergy cannot be created or destroyed. It can only be transferred from one store to another.

Energy input = energy output

The unit for measuring energy is the joule (J).

Flow Diagrams

Energy inputBattery (store of chemical energy.

Process

Energy outputLight energyThermal energy

Transferred electrically

Transferred by radiation/heating.

Sankey diagramsA simpler and clearer way of showing what happens to an energy input into a system. These should be to scale.

EfficiencyIn energy transfers a proportion of energy is wasted (transferred into stores other than the store require).

Preventing heat lossEfficiency means using as much energy produced as possible for the desired purpose.

Walls:● Two layered wall construction: thermal bricks (very good insulators) and outer wall.● An air gap between the two as air is a good insulator.● Glass fibre insulating wool a poor conductor that stops convection in the air gaps.● Surfaced with aluminium foil to reflect infrared radiation.

Glass:● Double glazed to trap a layer of air. ● Thickness is important - too thin then insulating effect is reduced but too thick then

convection currents will be able to circulate.

Roof insulation: ● Insulating panels trap layer of air.● Reflective foil to prevent heat loss via radiation.

Preventing heat loss 2Clothes:● They are insulators● Trap air around the body. It cannot circulate preventing convection and is a

very poor conductor. ● Sweat cannot evaporate meaning there is less cooling effect from sweating.

Thin high reflective blankets: ● Reflective surface reflects heat back into the body whilst the outer reflective

surface is a poor radiator of heat.Animals:● Birds fluff up feathers to increase the thickness of the trapped air layer

reducing heat loss via conduction. ● Penguins huddle as then less surface area of their bodies is exposed to the

cold.

ConductionThermal conduction is the transfer of thermal energy through a substance by the vibration of the atoms within the substance. The substance itself does not move.

1) If an area of a substance is heated the particles there gain kinetic energy and vibrate more rapidly.

2) They collide with each other transferring kinetic energy. 3) The energy spreads throughout the substance via this process.

Metals are better conductors because they have free electrons that can move easily through the structure colliding with the metal ions transferring energy.

(some metals have more than others)

ConvectionConvection is the transfer of heat through fluids by the upward movement of warmer, less dense regions of fluid.

1) Liquids and gases expand when they are heated. This is because the particles in fluids move faster and move apart.

2) The fluid in hot areas is less dense (they take up more volume) than the fluid in cold areas, so it rises into the cold areas.

3) The denser cold fluid falls into the warm areas. In this way, convection currents that transfer heat from place to place are set up.

Convector heater

Sea Breezes1) Energy is transferred by the sun to the land and sea.2) Air over the land is heated. The land heats up more quickly as it has a lower

specific heat capacity.3) Warmer air over land expands.4) Air becomes less dense and therefore rises.5) The cooler air above the sea becomes denser and sinks.6) It moves in to replace the hot air forming a convection current.

Land Breeze1) In the night the sea cools down more slowly than the land due to the high

specific heat capacity of water. 2) The air above the sea is warmer and therefore less dense causing it to rise.3) The land cools down more quickly as it has a lower specific heat capacity so

the air above it becomes cooler.4) The cooler air over the land is more dense and sinks and moves in to replace

the hot air forming a convection current.

Radiation● Thermal radiation is the transfer of energy by infrared waves.

● All objects emit and absorb infrared radiation.

● The hotter an object is, the more infrared radiation it emits.

● No particles are involved, unlike in the processes of conduction and convection, so radiation can work through a vacuum.

● This is why we receive heat from the Sun.

Emission and absorption of radiation

Surface Absorption Reflection Emission

Dark,matt, rough good poor good

Shiny, white, smooth poor good poor

Vacuum Flask● Rubber cap stops cooling by evaporation and reduces conduction.

● Silvery to reduce radiation.

● Double walled glass as it is a poor conductor.

● Vacuum prevents conduction and convection.

● Plastic outer wall as it is a good insulator.

Practical

Thermal energyThe sum of all the kinetic energy of molecules.

Measured in Joules.

Work and power

Work Energy is the ability to do work.

Work done, W (joules) = force,F (newtons) x distance moved,d (metres)

W = F x d

Work done = energy transferred

Gravitational Potential and kinetic energyGravitational potential energy = mass(kg) x gravity(N/kg) x height(metres)

GPE = mgh

If an object falls over its height is decreased and it has a lower centre of gravity so gpe is reduced.

Kinetic energy = ½ x mv2

PowerPower is the rate of transfer of energy or rate of doing work.

Power = Energy transferred/time takenP=E/T

Watt is the unit of power.

Electrical power = current x potential differenceP = VI

Electrical energy = ItV (time in seconds)E = QV

Kilowatt-hour kWh - A unit of energy.

Heating● As heat energy is applied kinetic energy is transferred to the particles.

● Temperature is the mean kinetic energy of molecules so as this increases temperature increases.

● As they gain more energy the bonds holding the particles together become weaker and break causing them to change state.

Energy resources and electricity generation

Non-renewable energy resourcesA non-renewable energy resource is one that cannot be replaced once it has been used. They will not replenish in a lifetime.

Examples include fossil fuels such as coal, oil and natural gas.

Coal power stationsAdvantages:

● Release a lot of energy.

Disadvantages:

● Non-renewable● Burning fossil fuels releases the greenhouse gas carbon dioxide.● This traps the Sun’s radiation causing global warming. ● Burning coal releases the most greenhouse gases whilst natural gas releases

the least.● Most types of coal and oil contain sulphur impurities.This reacts when burnt to

form sulphur dioxide. This forms acid rain. Whilst it is possible to remove sulphur or the sulphur dioxide produced, this is expensive.

● Power stations cannot be turned on quickly so cannot meet changes in demand.

Nuclear fuelAdvantages:

● No CO2 is emitted.● It does not produce greenhouse gases/polluting gases.● Does not contribute to global warming.● It is reliable.● There is a small volume of waste.● It is a concentrated energy source.● Power stations are relatively small.

Disadvantages:

● Nuclear waste disposal is difficult since it is radioactive and has a long half life and high activity..

● Risk of accidents causing radiation.● Nuclear power stations are expensive to build and decommission.● Nuclear power stations cannot be turned on quickly so cannot meet sudden variations in

demands.● Increasing security risk.

BiomassAdvantages:

● Renewable● Uses materials which would produce CO2 any way so no net emission● Reduces landfill● Relatively cheap

Disadvantages:

● Relatively inefficient● Can increase greenhouse gases● May require more land● High transport costs to collect raw material● Can be smelly● Variable output source● Storage costs for biogas

Renewable energy sourcesA renewable energy resource is one that will not run out.

Hydroelectric power1) The water in the reservoir has gravitational potential energy.2) As it flows down the hill the GPE is transferred mechanically to kinetic energy.

Advantages:

● It is a renewable energy source.● It does not produce polluting gases (it is a clean energy source).● They can meet changes in demand as it is a reliable energy resource.

Disadvantages:

● They can only be built in mountainous regions with enough rain.● It can damage the landscape and habitats for wildlife.● It can lead to flooding.

Wave and tidal powerWave energy advantages:● Wave energy is continuously available and is clean.● Quite efficient.

Wave energy disadvantages:● Expensive to set up.● Only suitable in coastal areas with large waves.

Tidal energy advantages:● It is continuously available.● It is a clean energy resource.● It is efficient.

Tidal energy disadvantages:● Damaging to environment.● Expensive.● Only suitable in coastal regions with large differences in low and high tide levels.

Wind PowerAdvantages:

● No air pollution.● Renewable energy source.● Relatively cheap operating costs.● Can be more efficient than conventional energy sources.● Local economy.● Abundant resource.

Disadvantages:

● Reliant on there being wind.● It can only be used in certain places. ● Wind farms cause environmental damage changing the appearance of the landscape.● They cause noise pollution and may kill birds. They are ugly.● They are costly to construct and many are needed to supply a city.

Solar power producing electricityPhotovoltaic cells transfer light energy to electrical energy.

Advantages:

● They are a renewable energy resource.● They are a ‘clean’ energy resource.● They are becoming cheaper.

Disadvantages:

● They are reliant on there being enough sunlight.● They are only 15% efficient meaning they are expensive in terms of how

much energy they produce.● They affect the appearance of the landscape. ● They take up a lot of land.

Solar power producing heatSolar heating systems can be used to heat small quantities of water.

They are designed to transfer energy to thermal energy through conduction, convection, and radiation.

They absorb radiation and use it to heat the water.

In the northern hemisphere they must face south and be angled so that the light falls on them as directly as possible.

Geothermal energy1) Thermal energy is transferred from hot rock to cold water.2) Water molecules gain kinetic energy.3) steam gains KE as it is heated by the rock4) Turbine gains kinetic energy from steam.5) Generator transfers kinetic energy into electrical energy.

Geothermal 2Advantages:

● It is a clean energy resource.● It is a renewable energy resource.● It provides direct heating.● Moderate costs.● Consistent energy source.● Does not take up a lot of space.

Disadvantages:

● It is only suitable for areas with thin crusts or high volcanic activity.

Supply and demandPredictable changes in demand include at the start of the day, when factories open and close and during winter.

Unpredictable changes include weather and if everyone decides to make tea during an ad break!

Turbines and generatorTurbine spins.

Coils of wire spin between the poles of magnets.

Current or voltage is induced in the coils of wire.

Solids, Liquids and Gases

Solids● Regular arrangement.

● Closely packed.

● Vibrate about fixed positions.

● Particles have strong forces of attraction so they cannot move.

● Little space between particles.

Liquids

● Irregular arrangement.

● The particles are touching but move past each other.

● The particles are arranged randomly.

● The forces of attraction between particles are smaller.

● Little space between particles.

Gases ● The particles in a gas move randomly at high speed.

● They move freely.

● The particles are much further apart.

● The forces of attraction are very weak.

● The particles have lots of kinetic energy.

Changes of StateWhen a substance is heated:

● the movement of its particles increases as they gain more kinetic energy.

● bonds between particles become weaker when a substance melts or evaporates, or sublimes to form a gas from a solid.

When a substance is cooled:

● the movement of its particles decreases as they lose kinetic energy.

● bonds between particles become stronger when a substance condenses or freezes.

Heating ice graph

A substance must absorb heat energy so that it can melt or boil. The temperature of the substance does not change during melting, boiling or freezing, even though energy is still being transferred.

This is because energy is used to break bonds between particles (latent heat).

Specific latent heat = the amount of energy needed to melt 1kg of a material.

Evaporation and condensationEvaporation● Temperature is proportional to the average kinetic energy of molecules● The particles in a liquid have different amounts of kinetic energy. ● Some will have enough energy to escape from the liquid and become a gas.● Remaining particles have a lower average kinetic energy than before - liquid cools down ● This is why sweating cools you down. The sweat absorbs energy from skin so that it can

continue to evaporate.

Condensation● The particles in a gas have different amounts of kinetic energy. ● Some may not have enough energy to remain as separate particles and come close

together forming bonds.● Energy is released when this happens. ● This is why steam touching your skin can cause scalds: not only is the steam hot, but

energy is released into your skin as the steam condenses.

Factors affecting it

● The rate of condensation increases if the temperature of the gas is decreased.

● The rate of evaporation increases if the temperature of the liquid is increased.

It is also increased if:

● The surface area of the liquid is increased

● Air is moving over the surface of the liquid.

● Wind causes rapid heat loss by forced convection. It makes air circulate close to the body surface. Causes sweat to evaporate from the skin more quickly causing rapid cooling.

Specific Heat CapacitySpecific heat capacity is the energy required to change the temperature of an object by one degree Celsius per kilogram of mass.

ΔQ = m x c x Δ𝜽

ΔQ - change in heat energy in Joules

m - mass in kilograms

c - specific heat capacity in J/kg℃

Δ𝜽 - change in temperature in degrees celsius

Practical - specific heat capacity of metals1) Connect an immersion heater to a 15V power supply.2) Connect a voltmeter in parallel and an ammeter in series.3) Take three types of metal with a hole drilled in them.4) Record the initial temperature of the metal.5) Put the heater in and record temperature, voltage and amps

every 30s.6) Calculate energy E=ItV and plot a graph of this against

temperature.

Insulation could be used to prevent heat loss to the surroundings.

Make sure heater has warmed up before putting it in.

Pressure

Pressure under a solid pressure, p (pascals) =

p =

1Pa = 1N/m2

Eg:

A knife cutting butter - The force is concentrated on a very small area which increases the pressure so the knife sinks into the butter.

Tank in mud - The force is spread over a large area which reduces the pressure so the tank does not sink into the mud.

DensityDensity = mass/volume

1) Measure the mass using scales. 2) Measure the volume using a displacement can. 3) Measure the volume displaced in a measuring cylinder.

Pressure in liquids and gasesPressure in gases and liquids at rest acts equally in all directions.

The particles in a liquid are moving at random and collide with any part of the container.They exert force and thus pressure on the walls of the container.

Atmospheric pressure is around 100,000Pa

Pressure and depthPressure in a liquid increases with depth.

pressure difference = height,h (m) × density,p (kg/m3) × gravitational field strength, g (N/kg).

p = h x p x g

The pressure at the bottom is highest so the force on the water is highest.

Boyle’s Lawp1V1=p2V2

P1 is the initial pressure

V1 is the initial volume

P2 is the final pressure

V2 is the final volume

Fixed mass of gas at constant temperature.

CompressingMolecules in a gas have random motion and are spread apart.

When a gas is squashed into a smaller container it presses on the walls of the container with a greater pressure,

This is because if the particles are squeezed into a smaller container the volume decreases. They will hit the walls more often exerting a force on the wall with which each one collides.

More collisions per second means a greater average force on the wall and thus pressure.

Gas pressure and temperature

Absolute ZeroAs we cool a gas the pressure keeps decreasing.

The pressure of a gas cannot become less than zero.

Therefore there is a temperature below which it is not possible to cool the gas further - absolute zero (-273℃)

The Kelvin scale starts from absolute zero.

The Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules.

To convert:

From celsius to Kelvin add 273.

From Kelvin to celsius subtract 273.

Absolute zero 2Pressure is proportional to temperature in Kelvin:

Pressure and Temperature 2

The volume of a gas within a container remains constant. When we heat a gas the kinetic energy of particles increases so they move at faster speeds. The movement of gas is random.Thus collisions with the walls of the container are harder and happen more often and pressure exerted increases.Conversely, as we cool a gas the kinetic energy decreases…At absolute zero the particles have no thermal or kinetic energy so cannot exert a pressure.

Magnetism and electromagnetism

Magnetism

MagnetsTwo like poles repel.

Two opposite poles attract.

Non magnetic materials are not attracted to magnets and cannot be magnetised.

Magnetic materials are attracted to magnets and can be magnetised.

A magnetically hard material is hard to magnetise and keeps its magnetism once it has been magnetised. It is useful as a permanent magnet. Eg Steel

A magnetically soft material is easy to magnetise and loses its magnetism easily. It is useful as a temporary magnet. Eg Iron

Magnetic fieldsA magnetic field is the volume of space where a magnetic force can be detected.

Magnetic field lines:

They show the direction of the magnetic force - the field lines travel from north to south.

They show the strength of the magnetic field - the field lines are closest together where the magnetic field is strongest.

They show the shape of a magnetic field.

PracticalMark scheme answer:

1) Place compass in the magnetic field and look were the needle points.

2) This line is marked using a pencil and paper method.

3) This is repeated in a different place to give a field line.

1) Place magnet under paper2) Sprinkle iron filings over.3) Tap the paper gently.

Overlapping magnetic fields

Uniform magnetic field

A uniform magnetic field is when the field is the same strength and direction everywhere.Lines should be parallel and the same distance apart from each other.

If the lines are moved closer together this indicates an increase in the strength of the magnetic field.

1) Two magnets.2) North facing South.3) Correct distance apart.

Induced magnetismIf we place an object made from a magnetic material inside a magnetic field it becomes a magnet.

We say that magnetism has been induced.

Electromagnetism

ElectromagnetismWhen there is a current in a wire a magnetic field is created around it. The field is weak and circular.

The strength of the magnetic field can be increased by increasing the current in the wire or wrapping the wire into a coil or solenoid.

The strength of the magnetic field is greater near the wire.

The right-hand grip rule determines the direction of the magnetic field.

Flat circular coil

Solenoid

The field produced by a solenoid is the same as a bar magnet.

Electromagnets1) Current carrying wire.2) Wrapped into a coil.3) Wrapped on iron core.

The strength of the solenoid can be increased ny:

1) Increasing the current in the solenoid.2) Increasing the number of turns on the solenoid.3) Wrapping the solenoid around a magnetically soft core such as iron.

.

They can be turn off and on.

Movement from electricityWhen a charged particle moves through a magnetic field it experiences force as long as its motion is not parallel to the field.

If the wire is placed between the poles of the uniform magnet, the two fields overlap.

The motor effect

1) Current in a wire produces a magnetic field. 2) This interacts with the magnetic field of the

permanent magnet. 3) The wire experiences a force in accordance

with Fleming’s left hand rule.● Below the wire the fields are in the same

direction and so reinforce each other and thus a strong magnetic field is produced here.

● Above the wire, the fields are opposite so a weaker field is produced.

● Therefore the wire feels a force pushing it upwards.

Fleming’s left hand ruleIf the current is reversed or the magnetic field is reversed the force will be reversed.

If the size of the current or the magnetic field is increased the size of the force will increase.

Suspended wiresCurrent in a wire produces a magnetic field.

The two magnetic fields interact and attract or repel.

When the current is reversed the magnetic field is reversed.

Like poles repel and unlike poles attract.

LoudspeakerUses the motor effect to transfer electrical energy to sound energy.

1) Electric currents from a source such as radio pass through the coils of a speaker.

2) These currents, which represent sounds, are always changing in size and direction.

3) A changing magnetic field (in strength and direction) is produced which interacts with the field of the permanent magnet

4) These fields apply rapidly reversing forces to the coil which cause the speaker cone to vibrate in accordance with Fleming’s left hand rule.

5) These vibrations are transferred to air creating the longitudinal sound waves we hear.

Loudspeaker

Electric motor1) Current in the coil creates a magnetic field around the wires of the coil.2) The coil’s magnetic field will interact with the field of the permanent magnet.3) One side will experience a force upwards and the other side will experience a

force downwards. Flemings left hand rule.4) This produces a turning effect.5) As the loop reaches the vertical position the momentum takes it past the vertical.6) In order for the rotation to continue the force on the wire must be reversed so that

the wire at the top is pushed down and the wire at the bottom is pushed up.7) This is done using a split-ring commutator to connect the coil to the electrical

supply.8) Its connections change every half turn reversing the current and thus the force.9) The coil will rotate continuously.

Electric motor

Electric motor diagram

To increase the rate at which the motor turns:1) Increase the number of

turns on the coil.2) Increase the strength of the

magnetic field.3) Increase the current in the

loop of wire.

Electromagnetic induction

Electromagnetic inductionMotors: convert electrical energy to kinetic energy.

Generators: convert kinetic energy to electrical energy.

When a conductor or magnet cuts through a magnetic field at right angles a voltage is induced.

If there is a complete circuit a current is induced.

You can increase the induced voltage by:

1) Moving the conductor more quickly.2) Increasing the strength of the magnet.3) Put more turns on your coil.

These alterations increase the rate at which field lines are cut.

Electromagnetic induction diagram

Generators1) A magnet rotates.2) This changes its magnetic field.3) The field lines are cut through the coil.4) Voltage is induced and therefore a current if there is a complete circuit.

Transformers1) Transformers step up or step down voltage.2) Current in the primary coil produces a magnetic field in the core.3) The current is alternating causing an alternating magnetic field.4) A soft laminated iron core is used to concentrate the magnetic field. Iron is

used since it is easy to magnetise and demagnetise.5) The secondary coil cuts the alternating magnetic field inducing an alternating

voltage in the secondary coil. 6) If the coil is connected to an appliance current in the secondary will be

induced.7) Transformers cannot work with DC since an alternating current and thus field

is required.

Transformers diagram

Step up and step down transformers1) Step up transformers increase voltage. They have more turns on the

secondary coil. More magnetic field lines are cut and thus a higher voltage is induced.

2) Step down transformers decrease the voltage. They have more turns on the primary coils.

3) Iron is easy to magnetise and demagnetise making it suitable since the magnetic fields are changing.

Transformer equations

Transformers in power transmission1) Step up transformers increase the voltage for transport of electrical power in

overhead cables.2) This reduces the current.3) This means that there is a small voltage drop in the wire with less energy lost as

heat since current produces a heating effect in wires.4) Due to the equation P=I2R if you reduce the current, power dissipation is reduced. 5) Using high voltages is more efficient. 6) The transformers have soft iron cores to improve efficiency.7) Step down transformers reduce the voltage and increase the current for usage.

They are safer and thinner insulation can be used.8) Overhead cables are good conductors with low resistance and a large diameter.

The National Grid is a network of cables that carry electrical energy from power stations to consumers.

Radioactivity and particles

Radioactivity

Atomic Structure

Charge = -1 Relative mass = 0

Charge = 0Relative mass = 1

Charge = +1Relative mass = 1

Atomic structure 2Atomic number, Z - the number of protons in an atom’s nucleus. (same as number of electrons).

Mass number, A - total number of protons and neutrons in the nucleus of the atom.

Mass number

Atomic number

Isotopes Isotopes are different forms of the same element which have the same number of protons but different numbers of neutrons.

Isotopes have a different ratio between protons and neutrons which affects the nuclear forces. Eg carbon-14

This makes the nucleus unstable.

This means it will eventually decay emitting energy and sometimes alpha or beta particles.

Ionising radiationRadiation is emitting energy as waves or subatomic particles.

When unstable nuclei decay they give out ionising radiation.

Ionising radiation causes atoms to gain or lose electric charge forming ions.

Unstable nuclei decay is a random process so you cannot predict or affect when it will happen.

Alpha (α) radiationAlpha radiation consists of relatively slow-moving particles emitted by unstable nuclei when they decay.

They consist of two protons and two neutrons (a helium nucleus)

Alpha particles have a short range.They can travel about 5 cm in air and cannot penetrate more than a few mm of paper.

They have a low penetrating power:1) This is because they have a higher charger and more mass meaning that they cause

more ionisation. 2) The force on the alpha particles is larger so the energy of the alpha is lost quickly. 3) They are more likely to collide with atoms. Alpha radiation is the most dangerous type of radiation if the source is inside the body as It is the most ionising type of radiation meaning it is absorbed by cells rather than passing straight through them.

Beta (β) radiationA β- particle is a very fast moving electron that is ejected by a decaying nucleus.

How is it emitted?1) The result of radioactive decay is to change the balance of protons and

neutrons in the nucleus to make it more stable. 2) β- decay involves a neutron in the nucleus splitting into a proton and an

electron.3) The proton remains in the nucleus and the electron is ejected as a β- particle.

Beta particles are less ionising as they are much smaller than alpha particles and they carry less charge.

This means that beta particles have a greater range - they can travel up to 10m in air and are absorbed by 2mm of aluminium.

Gamma (γ) radiationGamma rays are electromagnetic waves with the shortest wavelength and highest energy.

They are very weakly ionising as they have no mass or charge.

They have a very high penetrating power.

They travel at the speed of light.

Gamma rays can be absorbed by a number of centimetres of lead or about 1m of concrete.

Summary of properties

Neutron radiation● Neutrons are emitted by radioactive material.

● They have the same mass as a proton but no charge.

● If a neutron is absorbed by a nucleus the mass number goes up by 1 but the atomic number stays the same.

● As neutrons do not have a charge they do not directly cause ionisation.

● Neutrons are absorbed by other nuclei causing them to become radioactive.

● They are the only type of radiation to cause other atoms to become radioactive.

Investigating penetrating power of ionising radiation.1) Radioactive sources must be stored in lead-lined boxes and kept in a metal

cupboard with a radiation warning label. 2) The sources must be handled with tongs away from the body. 3) Before the source is removed measure the background radiation count over 5

minutes using a Geiger-Muller tube connected to a counter. Repeat this 3 times and calculate an average in becquerel.

4) Take a source of alpha radiation and set it up at a measured distance 2-4 cm.5) Measure the counts detected over 5 minutes. Repeat the counts with a sheet of

paper in front of the source. The counts will match the background radiation count showing it does not pass through paper.

6) Repeat with Beta and Gamma sources with aluminium and lead.

α decay equations In alpha and beta decay the atomic number will change meaning that alpha or beta decay causes the original element to transform into a different element.

Eg + energy

ꞵ- decay equationsEg

The radioactive isotope of carbon decays to form the stable isotope of nitrogen by emitting a beta particle.

Detecting ionising radiationPhotographic film can be used to detect ionising radiation.

The unit of radioactivity is the becquerel (Bq). It is a measure of how many unstable nuclei are disintegrating per second.

The Geiger - Muller Tube is also used.

Geiger-Muller tube

● The tube contains a mixture of gases at a very low pressure.● When ionising radiation enters the tube it causes the low pressure gas inside

to form ions. ● The ions allow a small amount of current to flow from the electrode to the

conducting layer which is detected by an electronic circuit. ● It is usually linked with a counter which gives a measurement in becquerels.

Background radiationBackground radiation is low-level ionising radiation that is produced all the time from a number of natural and artificial radioactive sources in the Earth.

Natural background radiation is due to the decay of naturally occurring isotopes in the earth that were formed when the solar system was created or from cosmic rays.

Artificial radiation comes from manmade sources.

Natural sources ● Radioactive isotopes in rocks in the Earth's crust.● One form of uranium decays very slowly producing the gases radon and thoron. ● Radon-222 is a highly radioactive gas.● In Cornwall, where the granite contains traces of uranium, the risk of exposure

to radiation from radon gas is greater. Radon is a dense gas that accumulates in the lower parts of buildings and can be inhaled. (alpha emitter)

● Nuclear reactions in stars and supernovae produce cosmic rays that hit the Earth. Our atmosphere prevents most rays but some reach the Earth’s surface.

● Carbon-14 and other radioactive isotopes are eaten by humans because they are present in all living things. (food and drink).

Artificial radiationNuclear power stations have been responsible for leaking radioactive into the environment.

Testing nuclear weapons in the atmosphere has also increased the amounts of radioactive isotopes.

Radioactive tracers are used in industry and medicine.

They are also used to treat cancer.

The majority of background radiation is natural.

Radioactive decayRadioactive decay is a random and unpredictable process.

It is possible to model radioactive decay using a coin tossing experiment although due to scale this experiment has limitations.

1) Take 1000 coins and throw them. 2) Remove the ones which land on heads and repeat.

This graph follows a rule: the smaller the quantity, the more slowly the quantity decreases.Exponential decay.Therefore whilst the process of decay is random there will be a probability that a certain fraction will decay in a particular time. We would expect the rate of decay to fall as time passes because there are fewer nuclei to decay.

The graph decreases steeply but then much more slowly.

Half lifeHalf life is the average time taken for half the nuclei (mass) in a sample to decay or for the activity of a sample to fall to half its initial value.

Every radioactive isotope has a different half life.

Some isotopes are very unstable and have a short half life whilst others are stable and have a long half life.

Measuring the Half life of a radioactive isotope● To measure the half life of a radioisotope we

must measure the activity of the sample at regular times using a Geiger-Muller tube linked to a rate meter.

● Before this measure the average background radiation and repeat this reading.

● We must subtract the background radiation from the measurements taken from the sample so we know the radiation produced by the sample itself.

● We then measure the rate of decay of the sample at regular time intervals.

Half life calculations

Use of radioactivity in medicine - TracersA radioactive tracer is a chemical compound that emits gamma radiation.

The tracer is swallowed by the patient or injected and its journey around the body can be traced using a gamma ray camera.

Different compounds are chosen for different diagnostic tasks:

Iodine-123 is absorbed by the thyroid gland in the same way as normal iodine. The isotope decays and emits gamma radiation allowing a gamma ray camera to produce a clear image of the gland.

The half-life of iodine-123 is about 13 hours. A short half-life is important as this means that the activity of the tracer decreases to a very low level in a few days.

Technetium-99 is the most widely used isotope in medical imaging. It is used to identify medical problems and can be used to produce 3D images of the body.

TreatmentRadiation from isotopes can have various effects on cells. Low doses of radiation may have no lasting effect.High doses may cause cells to stop working properly as the radiation damages DNA leading to cancer. Very high doses can kill living cells.Cancer can be treated by killing cancerous cells using chemicals containing radioactive isotopes. The radiation kills healthy cells as well as diseased ones. To reduce the damage to healthy tissue chemicals are used to target the location of the cancer. They may emit either alpha or beta radiation as they have a short range so only affect tissue close to the target.

Sterilization using radiationGamma radiation can kill bacteria and viruses.

It is used to kill these microorganisms on surgical instruments and other medical equipments.

The technique is called irradiation. The items to be sterilised are placed in secure bags to ensure they cannot be re-contaminated before used.

The gamma ray radiation will pass through the packaging and destroy bacteria without damaging the item.

Some food products are treated in a similar way to ensure they are free of bacteria which can cause food to rot or cause food poisoning.

Gamma rays are used due to their high penetrating power and because they are ionising enough to kill bacteria. (long half life - doesn’t need replacing).

Irradiation and contaminationIrradiation is exposing an object to nuclear radiation eg sterilization.

The object itself does not become radioactive because it only comes into contact with the radiation not the radioisotope itself. You are not contaminated with the source.

Radioactive contamination is when unwanted radioactive isotopes end up on other materials.The isotopes decay emitting ionising radiation.

Use of radioactivity in industry - Gamma radiography Gamma ray cameras can be used to examine the contents of luggage at airport.

A source of gamma radiation is placed on one side of the object to be scanned and a gamma ray camera is placed on the other.

The gamma rays pass through more objects than x-rays and can be used to check for faults in metal casting or welding. Without the gamma radiography neither the problem could be detected unless they were cut through.

An advantage of gamma radiography over x-rays for this is that gamma ray sources can be small and do not require a power source or large equipment.

GaugingIn industrial processes raw materials and fuel are stored in large tanks.

Radioactive isotopes can be used to gauge how much material there is in a storage container.

The coal absorbs a large amount of radiation so the reading on the lower detector will be small.As the upper part is empty it will have a high reading.

This methods means there is no contact with the material being gauged. Also optical gauging systems using light can be affected by coal dust.

Coal dust is much less dense so the gamma ray system still functions.

Gauging 2Gauging is used to measure the thickness of plastic sheeting. The thicker the sheet the greater the amount of radiation it absorbs and the amount passing through get smaller.

By measuring the amount of radiation that passes through the sheeting its thickness can be controlled during manufacture.

Smoke alarmsOne type of smoke detector uses americium-241, a source of alpha radiation. to detect smoke.

The alpha particles pass between the two charged metal plates, causing air particles to ionise (split into positive and negative ions). The ions are attracted to the oppositely charged metal plates causing a current to flow.

When smoke enters between the plates some of the alpha particles are absorbed causing less ionisation to take place.This means a smaller than normal current flows so the alarm sounds.

Tracing and measuring the flow of liquids and gasesRadioisotopes are used to check the flow of liquids in industrial processes.

Very small amounts of radiation can easily be detected. Complex piping systems, like those in power stations can be monitored for leaks.

Radioactive tracers are also used to measure the rate of spread of sewage.

Radioactive dating1) Cosmic rays with a lot of energy continually strike the Earth.2) When they hit atoms of gas in the atmosphere the nuclei of atoms break apart

colliding with other atoms turning elements in the air to different isotopes. 3) One collision involves a fast-moving neutron striking an atom of nitrogen to

form carbon-14.4) Carbon-14 atoms react with oxygen to form carbon dioxide just like

carbon-12. The carbon dioxide is absorbed by plants in photosynthesis.5) A proportion of carbon that makes up any plant will be carbon-14. 6) Therefore it enters the food chain which means that animals and humans will

also have a proportion of carbon-14 in our bodies.

Radioactive dating 21) These carbon-14 atoms will decay but are continuously replaced.

2) When an organism dies the replacement process stops and the radioactive carbon decays and the proportion of carbon-14 to stable carbon decreases.

3) The half-life of carbon-14 is ≈ 5600 years. This means that every 5600 years the proportion of carbon-14 in a dead plant or animal will halve.

4) The amount of carbon-14 present in a sample of a dead plant or animal is found by measuring its activity.

5) This is compared with the amount of carbon-14 that would have been present when the sample was part of a living organism.

6) From this it is possible to estimate when the source of the sample died.

Radioactive dating 3

There are limitations to this method:It assumes the level of cosmic radiation is constant which is not necessarily accurate. The technique has been adjusted to take variations of cosmic ray activity into account by testing samples of a known age like material from mummies or from very ancient living trees.The radiocarbon method is not used to date samples older than 50000-60000 years becauses after 10 half lifes the amount of carbon-14 is too small to measure precisely.

Dangers of ionising radiationIonising radiation can cause damage to cells and tissue. Whilst cells can repair or replace themselves if cells suffer repeated damage the cell may be killed.

The cells may mutate due to damage of DNA and divide uncontrollably causing cancer.

Alpha particles have the greatest ionising effect but as they cannot penetrate skin alpha sources pose little risk. However, if the source is taken into the body either by inhaling or on food the radiation will be very close to living cells and they may be damaged if exposure is prolonged.

Radon gas is a decay product of radium and is an alpha emitter. Smokers greatly increase their exposure to this as the radiation source is drawn into the lungs as cigarette smoke contains radon.

Safe handling of radioactive sources in industryIn the nuclear industry and research laboratories much larger amounts of radioactive material are used.

Very energetic sources will be handled remotely by operators who are protected by lead shields, concrete and thick glass viewing panels.

Neutron radiation is absorbed by lighter elements and waste materials - spent uranium fuel rods from nuclear reactors are stored under water until neutron radiation levels drop to a safe level.

The main problem with nuclear materials is long-term storage. Some materials have very long half-lives so remain active for thousands of years. Nuclear waste must be stored in sealed containers that must be capable of containing the radioactivity for long periods of time.

Fission and fusion

Nuclear reactionsNuclear reactions, including fission, fusion and radioactive decay, can be a source of energy.

Nuclear fission1) A U-235 nucleus absorbs a slowing moving neutron.2) An unstable nucleus is formed.3) This nucleus splits into two radioactive daughter nuclei.4) Energy (KE) and more than one neutron is released.

Chain reactions1) These neutrons are absorbed by other

nuclei causing more fissions in chain reaction.

2) In a nuclear bomb two pieces of fissile material which are smaller than the critical mass are forced together under high pressure to form a mass greater than the critical mass. This leads to a chain reaction.

In nuclear reactors1) A moderator is used to slow down neutrons by absorbing some of their kinetic energy

so that they can be absorbed by uranium allowing fission to continue.2) Control rods absorb neutrons to control the rate of fission. They can be inserted and

removed. If they are removed fewer neutrons will be absorbed so the rate of fission will increase rapidly. Too much energy will be released resulting in meltdown of reactor.

3) The energy produced is used to heat water.4) The steel vessel + concrete prevent radiation escaping.

Nuclear fusionIn nuclear fusion hydrogen isotopes collide to form helium, a neutron and a lot of energy.

Two very small nuclei create a larger nuclei resulting in a loss of mass from smaller nuclei accompanied by a release of energy.

Fusion is the source of energy for stars.

Nuclear fusion difficultiesNuclear fusion cannot occur at low temperatures and pressures.

The two nuclei are both positive so repel each other.

The electrostatic repulsion of protons must be overcome to allow them to collide requiring very high temperatures and pressures.

Astrophysics

Motion in the universe

SpaceThe Universe is a collection of billions of galaxies.

A galaxy is a large collection of billions of stars.

Our solar system is in the Milky Way galaxy which has about 100 billion stars.

The planets

My Very Educated Mother Just Served Us Nine Pizzas.

GravityPlanets and comets travel around the Sun.

Moons and satellites travel around planets.

Newton suggests that between any two objects there is always a force of attraction which he called gravitational force.

He stated that the size of this force depends on the:

1) Masses of the two objects.2) Distance between the masses.

Gravity 2The gravitational attraction between objects with small masses is tiny.

The force of attraction is only obvious when one or both of the objects has a very large mass eg a moon or planet.

The Sun is massive and contains over 99% of the mass of the Solar System. It is the gravitational attraction between this mass and the planets that holds the Solar System together and causes the planets to followed their curved paths.

The planets closest to the Sun have the greatest attraction so follow the most curved paths whilst the planets furthest from the sun have the weakest attraction and follow the least curved paths.

The Planets

Satellites and MoonsA satellite is an object that orbits a planet. They can be natural or artificial.

Natural satellites are called moons.

All moons have circular orbits because of the gravitational forces between them and their planet.

Artificial satellites:

Allow us to communicate over large distances.

Some satellites are put into lower orbits are used to monitor the Earth’s surface, such as temperature of oceans or progress of forest fires.

CometsComets are large rock-like pieces of ice that orbit the Sun.

They have very elliptical orbits which at times take them very close to the Sun.

At other times they travel close to the edge of the Solar System.

Gravitational field strengthThe strength of gravity on a planet or moon is called its gravitational field strength,g.

The larger the mass of a planet the greater its gravitational field strength.

The larger the radius of a planet the smaller the gravitational field strength at its surface.

The gravitational field strength is approximately 10N/kg whilst on the Moon it is approximately 1.6N/kg.G.f.s = weight/mass

This means on the moon you weigh six times less.

On Jupiter you would weigh 2.5 times more.

OrbitsPlanets have nearly circular orbits.

Moons have circular orbits.

Comets have very elliptical orbits.

Orbital speeds of planets and satellites

= orbital speed,v = v

For planets r is the average distance from the sun.

Stellar evolution

Classifying starsA star’s colour is related to its surface temperature.

Brightness of the starsThe brightness of a star depends on:

● Its distance from the Earth.● Its luminosity.

There are three different ways to describe the brightness of a star:

1) Apparent brightness or magnitude - how bright as seen from earth.2) Absolute brightness or magnitude - How bright stars would appear if

placed at the same distance from earth (standard distance).3) Luminosity - How much energy in the form of light is emitted from a star’s

surface every second.

Star cycle1) A nebula is formed when dusts and gas particles are drawn together by

gravity.2) Compression of particles increases pressure and temperature allowing

nuclear reactions to begin. Protostar.3) Nuclear fusion of hydrogen occurs to form helium and energy during the main

lifespan of the star. Forces of expansion and contraction are balanced.4) At the end of the stable period hydrogen fusion stops. Gravity is the largest

force and the star compresses increasing the temperature. This is so high that fusion of helium begins.

5) The star expands and cools forming a red giant.6) As helium fusion stops the star collapses and increases in temperature to

from a white dwarf.7) The white dwarf star cools into a black dwarf.

Stars bigger than the sun1) After the stable period it expands to form a red supergiant.2) After this it collapses into a supernova.3) This will become a neutron star or black hole (if it is really heavy).

Bigger stars have a higher pressure. Therefore there is more rapid fusion and a shorter lifespan.

Smaller stars stay on the main sequence longer.

Comparison of two types1) All main sequence stars fuse hydrogen into helium. 2) Lower mass stars stay on the main sequence longer. 3) Lower mass stars become red giants.4) Higher mass stars become red supergiants. 5) Red giant become white dwarf.6) Red supergiant becomes a supernova.7) Supernova become a neutron star or black hole.

Hertzsprung-Russell diagram

Cosmology

Doppler EffectWhen the ambulance is moving, the wavefronts ahead of the car are compressed.

The waves will have a shorter wavelength and a higher frequency.

Person B hears a sound that has a higher pitch.

Person A hears a lower pitch as the wavefronts are more stretched out so so have a lower frequency.

A B

Doppler effect● The dark lines are called absorption lines.

They are frequencies of light that have been absorbed by hydrogen.

● You can see that as distance increases the lines move towards the red part of the spectrum.

● This is called ‘red-shift’.● Red-shift indicates that the source is

moving away from the observer.● Blue-shift indicates that the source is

moving towards the observer.

Red-shift and the Big Bang TheoryAlmost all galaxies emit light with red-shift.

The further a galaxy is aware the greater the red-shift and therefore the faster it is moving away from us.

Therefore scientists believe that the Universe is expanding and that the Universe was in one place at the start.

The Doppler equation

HubbleHubble discovered that:

1) All distant galaxies are receding and almost all near ones.

2) The fastest galaxies are the furthest away.

3) Their recessional velocity is directly proportional to the distance.

Cosmic Microwave Background RadiationThe Big Bang would have released energy in the form of waves.

These waves would have been stretched and would have much longer wavelengths now than before.

It was predicted this would be in the microwave part of the spectrum

Background radiation was detected in all directions in the Universe.

Experiment errorsParallax error

Zero error

Calculation error