PhysicsPhysics© WebTeachers 2010

Static Electricity

When some materials are rubbed together they become charged.

• Friction between the two materials causes electrons to be removed from one of them and added to the other.

• When a material gains electrons it becomes negatively charged.

• The material that loses electrons becomes positively charged.

• If the material is an insulator, these charges remain at the point they are produced.

• This is then called static electricity.

Examples of static electricity in action

Charged objects interact with each other:

LIKE charges REPEL

UNLIKE charges ATTRACT

+ + + -

Current ElectricityElectric current is the flow of charged particles (electrons) through a circuit.

Electric charges can move through some materials:

• materials that are electrical conductors will allow charges to flow away from the point where they start

• good conductors e.g. metals, will allow charges to move through them freely.

• the flow of charged particles through the conductors in a circuit is known as an electric current.

• for an electric current to flow we need a power supply and a complete circuit.

The electric current that flows around an electric circuit is a flow of charged particles called electrons:

• the electrons transfer energy from the power supply to the components in the circuit.

• the current is measured in units called amps (A) and can be measured using a device called an ammeter, placed in series with components.

• the current that leaves a component is the same as the current that enters it.

• the current is not used up by the components in the circuit - they use the energy carried by the current.

• we follow the convention that current flows from the positive terminal of the power supply to the negative end (although electrons, being negatively charged, actually move the other way).

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+

Conventional current flowMovement of electronsVoltage (Potential Difference)

Voltage is the electrical ʻpushʼ given to the charges (electrons) in the circuit.

The voltage represents a difference in electrical energy between two points in a circuit:

• the bigger the difference in energy, the bigger the voltage.• voltage is also known as potential difference (p.d.).• voltage is measured in units called volts (V).• voltage can be measured using a device called a voltmeter.• to measure the voltage across a component in a circuit, you must connect a voltmeter in

parallel with it.• you can measure the voltage across a cell or battery - the more cells, the bigger the

voltage (as long as they are connected the right way round).• the cell or power supply transfers energy to the charges, and pushes them through the

wires and components. If you take the cell away, the charges are not pushed through the circuit any more and the components do not work. If you add more cells, more energy is transferred to the charges.

ELECTRICITY & MAGNETISMCircuits - Current & Voltage

Series Circuits

(Arrows show direction of current flow)Features of a Series circuit

• There is only one current path between the power supply terminals.

• A switch placed anywhere in the circuit will affect all of the components in the circuit.

• The current is the same at all points in the circuit.• The current flowing in the circuit depends on the

power supply and the number and type of components in the circuit.

• Increasing the voltage of the power supply will increase the current.

• Adding more components will reduce the current, as there will then be more resistance in the circuit.

• If a component in the circuit breaks then the circuit will cease to work, as there is only one current path and therefore no longer a complete circuit.

Parallel Circuits

(Arrows show direction of current flow)Features of a Parallel circuit

• There is more than one current path between the terminals of the power supply.

• A switch will only affect the components in the same current path.

• The current splits at a junction in the circuit and rejoins when the branches meet again.

• The current is not the same at all points in the circuit.• The current in each branch of the circuit depends on

the components in that branch.• If a component in one branch of the circuit breaks it

will not affect the other branches, as they are separate current paths and so they still form a complete circuit.

• Each branch of the circuit gets the full ʻpushʼ from the power supply voltage.AND/OR Circuits and Truth Tables

Switch A Switch B Lamp

Open Open Off

Closed Open Off

Open Closed Off

Closed Closed On

AND Circuit

Lamp is on when Switch A AND Switch B are closed

Switch A Switch B Lamp

Open Open Off

Closed Open On

Open Closed On

Closed Closed On

OR Circuit

Lamp is on when Switch A OR Switch B are closed

ELECTRICITY & MAGNETISMCircuits - Types of Circuits

In this circuit, when the switch is closed, we say that the lamp lights to normal brightness - one cell is supplying energy to one lamp.

Using this idea, and assuming that all cells and lamps are the same, look at the following circuits....

Building Basic Circuits

In this circuit the buzzer should sound and the lamp should light to normal brightness, as the circuit is complete and the current flows through both components.

If we now connect an extra piece of wire around the lamp as shown, the buzzer will sound but the lamp will no longer light. This is because the current will take the route with least resistance - the new piece of wire with no component.We call this a short circuit.

Short Circuits

In this circuit, the motor is being short-circuited by the wire running diagonally from the top-left to bottom-right of the circuit. The motor will therefore not work as the current flows along this wire.

In this circuit an extra parallel branch has been included (often a mistake made by pupils when drawing parallel circuits). The extra branch actually creates a short circuit and none of the lamps light up.

When building any kind of circuit it is vital that the circuit is complete - this means that the circuit contains an appropriate power supply and all of the necessary components (lamps, motors, buzzers etc.), connected together by wires without any breaks in the circuit. Any gaps in the circuit will prevent current from flowing.

Complete Circuits

When designing circuits on paper we use circuit symbols to represent components, rather than draw out a full picture of each component. The symbols make it easy to map out circuits and to understand how they work. It is important to know a range of circuit symbols for your physics exam.

Circuit SymbolsELECTRICITY & MAGNETISM

Circuits - Constructing Circuits

Measuring Current Measuring Voltage

In order to measure current we have to:

• use a device called an ammeter• connect the ammeter in series with the circuit components• remember that in a series circuit the current will be the

same at all points in the circuit• remember that in a parallel circuit the current splits up at a

junction and re-combines when the branches join up again

• remember that current is measured in amps.

Series: Current the same at all points in the circuit

A1=A2=A3

Parallel: Current entering junction is the same as current leaving the junction

A1=A4Current splits at the junction and recombines

afterwards i.e. A1=A2+A3 and A2+A3=A4

ASymbol for an ammeter is

In order to measure voltage across a component we have to:

• use a device called a voltmeter• connect the voltmeter in parallel with the

component• remember that voltage is measured in volts.

VSymbol for a voltmeter is

Voltmeter is placed in parallel with the component - this shows the voltage across the component

Although you may often use analogue ammeters and voltmeters to measure current and voltage in the school laboratory, digital multimeters can do the job of both when connected correctly in the circuit. They can be used to measure resistance too.

Digital Multimeters

An analogue ammeter

An analogue voltmeter

Energy Transfers in Circuits

• A cell or a battery is a store of chemical energy• In a complete circuit, this chemical energy is converted

into electrical energy, which is moved around the circuit by the current.

• In this way the energy is transferred to other devices in the circuit.

• The other devices in the circuit change the electrical energy into different forms.

e.g. lamp transfers electrical energy into light energy, buzzer transfers electrical energy into sound energy etc.

Several energy transfers take place in electrical circuits:

ELECTRICITY & MAGNETISMCircuits - Measuring

Current & Voltage

Poles of a MagnetWhen a piece of magnetic material (e.g. iron, steel, cobalt, nickel) is magnetised we call it a magnet.• All magnets have two poles, the north-seeking

pole (north pole for short) and the south-seeking pole (south pole for short).

• Every magnet has a space around it where it exerts a force on other magnets or other magnetic materials.

• The poles are where the magnetic force is strongest.

• Magnets exert forces on other magnets - opposite magnetic poles exert a force of attraction on each other; similar magnetic poles exert a force of repulsion on each other.

Remember: LIKE POLES REPEL, UNLIKE POLES ATTRACT

Also be aware that repulsion is the only true test for a magnet - you can only show that an object is a

magnet if it repels a known magnet.

The Field Around a Bar Magnet

The Earthʼs Magnetic Field

ELECTRICITY & MAGNETISMMagnetic Fields

The Magnetic field around a bar magnet can be described by field lines as shown on the diagram below:

The field pattern is out of the North and into the South

The field around a bar magnet can be investigated using a plotting compass to track the field lines as shown below:

The field pattern can also be viewed using iron filings. When iron filings are sprinkled onto a sheet of card above a bar magnet, the filings line up in the pattern of the magnetic field:

Permanent MagnetsBar magnets are permanent magnets. This means that their magnetism is there all the time and cannot be turned on or off.

The field is strongest at the poles where the field lines are most concentrated

The Earth has a magnetic north pole and a magnetic south pole. It behaves as though it has a giant bar magnet inside it. Bar magnets can line up in the Earth's magnetic field and point north - this is what allows a compass to work.Remember that the north pole of a bar magnet is actually called the 'north-seeking pole', and it points to the Earth's magnetic north pole, while the ʻsouth-seeking poleʼ points to the Earthʼs magnetic south pole.

Magnetic Fields Due to Current Carrying Wires The Field Produced by a Coil

Constructing an Electromagnet

Uses of Electromagnets

ELECTRICITY & MAGNETISMElectromagnets

Power Supply

Switch

Power Supply

When an electric current flows there is a magnetic field associated with it and this can be demonstrated using the setup shown below. When the circuit is switched on, the current flows through the wire and iron filings or plotting compasses placed on the cardboard around the wire line up, in the pattern of the magnetic field caused by the current. It is a pattern of concentric circles around the wire.

+ -

When a coil of wire (solenoid) is connected to a power supply and a current passed through it, the magnetic field pattern produced is the same as that of a bar magnet. If plotting compasses are used to investigate the field pattern the familiar arrangement of field lines running out of the north and into the south is produced. If the power supply is reversed though, the field pattern is also reversed.

A magnetic field is produced when an electric current flows through a coil of wire. This is the basis of the electromagnet. Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off just by turning the power supply on or off.

The strength of an electromagnet can be increased in three ways: 1) Adding more turns to the coil of wire2) Increasing the current through the coil3) Wrapping the coil around an iron core

A simple electromagnet can be made by winding wire around a nail very tightly. The more windings, the stronger the magnet, but the ends should be left free. There should be only one layer of wire on the nail. The ends of wire are then connected to a battery. Now paper clips, staples, and even other nails can be picked up. When the battery is disconnected, the electromagnet is turned off. The nail may still be a bit magnetized, but it will soon wear off. If the electromagnet is left on for too long; it will quickly get hot and drain the battery.

There are a number of uses of electromagnets. They are found in loudspeakers, relays, electric motors, lifting magnets in scrapyards, electric bells etc.Examining how the electric bell works in useful in understanding the uses of electromagnets:

GongHammer

Sprung metal arm

Electromagnet

When the switch is pressed, the circuit is complete and the current flows through the electromagnet setting up a magnetic field, which attracts the metal arm towards it. This causes the hammer to hit the gong but breaks the circuit, cutting off the current and switching off the electromagnet The arm then springs back to its original position which completes the circuit again. This process continues until the switch is released.

Types of Force & their Effects Balanced & Unbalanced ForcesSpeed and its Measurement

Frictional Forces

Five things forces can do to an object:• Speed it up• Slow it down• Change its direction• Change its shape• Turn it

Types of force include friction, gravitational force, reaction force from a surface or the ground (ground reaction force) or from a liquid (upthrust), stretching forces, tension and air resistance (often called drag).

FORCES & MOTIONForce and Linear Motion

When two forces acting on an object are equal in size but act in opposite directions, we say that they are balanced forces. If the forces on an object are balanced (or there are no forces acting on it):• the object stays still, if it is not already moving• the object continues to move at the same speed and in

the same direction, if it is already moving.

weight

ground reaction force

Car not moving(balanced forces)

ground reaction force

weight

drivingforce

of engine

friction and air

resistance

• Forces are just pushes and pulls• You canʼt see a force but you can see the effects of

a force.• Forces are measured in Newtons (N).• Forces usually act in pairs.• A Newton meter (forcemeter) is used to measure

forces.

Car moving atconstant speed(balanced forces)

ground reaction force

drivingforce

of engine

friction and air

resistance

Car accelerating(unbalanced forces)

weight

In the last diagram (above), the forces are unbalanced as the driving force is greater than the frictional forces, so the car accelerates. If the frictional forces were greater than the driving force (by braking for example), the forces would once again be unbalanced, but this time the car would slow down (decelerate).

To work out the speed of an object, we need to know:

• the distance the object has travelled• the time taken to travel that distance

The formula for calculating speed is:

The unit of speed in physics is the metre per second (m/s), as distance is measured in metres and time is measured in seconds, although you may have to use kilometres per hour (km/h) for some problems.

Whenever an object moves against another object or surface, it is likely to experience frictional forces. These are forces that act in the direction opposite to the direction of movement of the objectFrictional forces are much smaller on smooth surfaces than on rough surfaces, which is why we slide on ice.

Friction can be useful - grip on shoe soles stops slipping, tread on car tyres helps grip the road, brakes on vehicles stop the vehicle using friction.

Friction can be a nuisance - when there is a lot of friction between moving parts, energy is lost to the surroundings as heat and the parts wear out, friction slows us down when we want to go faster.

So, to increase friction, we make the surfaces rougher (e.g. more grip) and to reduce friction we make the surfaces smoother (e.g. streamlining or lubrication).

Air ResistanceAir resistance is caused by the frictional forces of the air against an object travelling though it. The faster the object (e.g. a vehicle) moves, the bigger the air resistance becomes. It is often called drag.

weight

air resistance (drag)When this skydiving sheepʼs air resistance & weight are balanced, his speed remains constant (terminal velocity). Opening his parachute increases drag, slowing him down until he reaches a new terminal velocity, which is a safe speed for him to land.

Gravitational Force Mass and Weight

Stretching Objects

FORCES & MOTIONGravitational Force &

Stretching

MassThe mass of an object is the amount of matter it contains. The more matter an object contains, the greater its mass. Mass is measured in kilograms (kg) but it is often easier to measure mass in grams (g). An object's mass stays the same wherever it is.

WeightThe weight of an object is the result of the gravitational force between the object and the Earth. The greater the mass of an object, the greater its weight. Weight is measured in newtons (N) as it is produced by a force (gravity).On Earth, an object with a mass of 1 kg has a weight of 10 N. So, to find the weight of any object in Newtons, we multiply its mass by 10.Remember that the mass of an object stays the same wherever it is, but the weight of the same object can change. This happens if the object goes somewhere where gravity is stronger or weaker, such as into space.i.e. a person with a mass of 60 kg will have a weight of 600 N on Earth - in space the personʼs mass will still be 60 kg, but their weight will be 0 N (zero gravity in space); on the Moon the personʼs mass will still be 60 kg but their weight will be 100 N as the Moon has one sixth of the Earthʼs gravity.

All objects have a force of attraction between them, that attracts them towards each other. This force is called gravity. Gravity only becomes noticeable though when there is a really massive object involved, like a planet, moon or a star.The size of the gravitational force depends on the masses of the objects involved and the distance between them - the greater the masses and the closer together they are, the bigger the gravitational force.The Earth has more mass than the Moon, so the gravitational force is greater on the Earth than it is on the Moon. The Earth's gravitational force pulls objects towards the centre of the Earth. This is what gives objects their weight - weight is the pull of gravity on an objectʼs mass.Gravity is the force that keeps the Moon in orbit around the Earth and keeps the planets in orbit around the Sun.

Some objects can be stretched or compressed when a force is applied to them (e.g. hanging a weight from a spring). Bodies which are able to change shape when a force is exerted on them and return to their original shape when the force is removed are said to be elastic.

Stretching Springs

A spring with no weight attached will have a particular length (original length) if it has not been deformed (stretched beyond its limit of proportionality).

When a single spring has a weight (load) hung from it, the

extension of the spring is proportional to the load applied.

i.e. the greater the load the greater the extension

When two springs are connected in series, the extension produced is still

proportional to the load, but each spring stretches as much as one on

its own, so the extension is doubled.

When two springs are connected in parallel, they share the load and so the extension is half of that of a single spring with the same weight applied.

Remember, in each case:Extension = New length - Original length

For Springs in Series:Total Extension = Extension of one spring x N

For Springs in Parallel:Total Extension = Extension of one spring ÷ N

(Where N is number of springs)

FORCES & MOTIONForce and Rotation

Levers and Simple Machines

Moments

Simple machines make work easier for us by allowing us to push or pull over increased distances. Here are some examples of simple machines:

PulleyA pulley is a simple machine that uses grooved wheels and a rope to raise, lower or move a load.

LeverA lever is a stiff bar that rests on a support called a fulcrum which lifts or moves loads.

WedgeA wedge is an object with at least one slanting side ending in a sharp edge, which cuts material apart.

Wheel & AxleA wheel with a rod, called an axle, through its center lifts or moves loads.

Inclined PlaneAn inclined plane is a slanting surface connecting a lower level to a higher level.

ScrewA screw is an inclined plane wrapped around a pole which holds things together or lifts materials.

In the above examples, each machine makes work easier to do by providing some trade-off between the force applied and the distance over which the force is applied.

Forces can make objects turn if there is a pivot. The moment of a force is a measure of the turning effect (or torque) produced by a force acting on an object.Example: Think of a see-saw. When no-one is on it the see-saw is level, but it tips up if someone gets onto one end. It is possible to balance the see-saw again if someone else gets onto the other end and sits in the correct place. This is all due to moments.To work out a moment, we need to know:• the force or load applied• the distance from the pivot that the force or load is applied

The general formula for working out moments is:

moment = force x distance

(Remember that the distance in this formula is the distance of the force from the pivot.) The unit of moment is Nm (newton metre).

Example 1In the example below, a see-saw has been set up and a 4 Newton load has been placed 0.4 metres from the pivot:

Using the formula for moments:moment = force x distance

it is clear that the moment (or turning effect) on this see-saw is...

moment = 4 x 0.4 = 1.6 Nm

Example 2In the example below, a see-saw has been set up and a 5 Newton load has been placed 0.5 metres from the pivot. This time we need to work out the size of the force required to balance the see-saw, when placed 0.25 m away from the pivot, on the other side:

To work this out we need to consider the moments on each side of the pivot. When moments work in opposite turning directions, we often refer to them as clockwise and anti-clockwise moments. So...

Clockwise moments = F x d = 5 x 0.5 = 2.5 NmAnti-clockwise moments = F x d = F x 0.25

For the see-saw to balance, the clockwise and anti-clockwise moments must be equal. Therefore...

F x 0.25 = 2.5and so... F = 2.5/0.25 = 5 N

FORCES & MOTIONForce and Pressure

Pressure and its Application

Pressure is the force acting over a certain area. The formula for pressure is:

Pressure = ForceArea

Pressure is measured in units of N/m2

(newton per square metre), but another unit may also be used. This is called the pascal, Pa. (1 Pa = 1 N/m2)

Many exam questions also deal with pressure in N/cm2, usually because a square metre (m2) is such a large area to work with when dealing with everyday situations.

From the formula, it is clear that the greater the area over which a force acts, the lower the pressure. This can be seen in a practical situation by considering the use of a drawing pin:

Drawing pins have a large round end for you to push the sharp end into a notice board. The round end applies a low pressure to your thumb, but the sharp end applies a high pressure to the notice board, so it pushes in.

Pressure in Liquids

Relationship between Force, Pressure and Area

Another simple example of how pressure works can be seen by examining the boxes above. Both boxes have the same weight (100N), but the first box lies on one of its sides which has an area of 2m2, causing a pressure of 50 N/m2. The second box lies on one of its sides which has an area of 1m2, causing a pressure of 100 N/m2. So, although both boxes have the same weight, the pressure they cause is different due to the area of their contact sides.

Pressure acts in all directions in a liquid but the deeper you go, the greater the pressure. This is why dams are wider at their bases than at the top.

Force spread over a greater area reduces pressure...

Concentrating force over a smaller area increases pressure...

Hydraulic equipment and machines use the fact that pressure is transmitted though a liquid to benefit us. A small force applied at one point can be used to create a larger force at another point, due to the hydraulic pressure within the system e.g. car breaks.

LIGHT & SOUNDThe Behaviour of Light

- Light & Sight

Luminous Sources

The Way Light Travels How We See Objects

Light is produced by luminous objects, such as fires, electric lamps and stars like the Sun.

The light that we can see is called visible light, but there is also light that we cannot see, including ultraviolet light and infrared light.

Visible light is a type of radiation and forms a small part of the Electromagnetic Spectrum, which shows all types of radiation and the wavelengths associated with the different types. Although we can only see the visible part of the spectrum, we use other types of radiation in various ways, although some types are dangerous to us.

Light travels very much faster than sound, which is why you see lightning in a thunderstorm before you hear the thunder clap. It travels at 3 x 108 m/s (in other words 300,000,000 m/s).Light travels in straight lines. It cannot bend around corners, so we cannot see around a corner unless we use a mirror. We get shadows because light cannot bend round behind an object.Light cannot travel through opaque objects, such as brick walls. Opaque objects can cast dark shadows when light is shone on them. Light travels through transparent objects, such as glass windows. Paper and other translucent objects let some light through, but not all of it. This is why you can see the typing on the other side of a piece of printed paper if you hold it up to a light.

We see objects because light reflected from them enters our eyes. The light from luminous objects such as stars and lamps may enter our eyes directly. Non-luminous objects do not make their own light, but we can still see them if light from a luminous object reflects or scatters off them into our eyes.

Light travels from the light source to the non-luminous object

Light also travels from the light source directly to our eyes

Light reflects off the non-luminous object to our eyes, allowing us to see the object

LIGHT & SOUNDThe Behaviour of Light

- Reflection & Refraction

Reflection Refraction

Dispersion

Colour, Colour Objects and Colour Filters

Light can bounce off surfaces. We call this reflection and we say that light reflects off surfaces.Mirrors are very smooth and shiny. They reflect light evenly and we can see an image in them. A flat mirror is called a plane mirror.Bumpy or rough surfaces do not reflect light evenly. Instead, the light is scattered in all directions, and usually we cannot see an image. This is why you canʼt brush your hair in front of a brick wall.

There is a rule about how light behaves at plane mirrors:

Angle of incidence = Angle of reflection

Light normally travels in straight lines, but it can bend at the boundary between two materials with different densities e.g. light passing from air into a dense glass block will bend slightly. This is called refraction.

Refraction causes some interesting effects, such as making a ruler look like it is bent when part of it is placed into a bowl of water and making ponds look shallower than they really are.White light can be split up to form a spectrum by using a prism. A prism is

a triangular block of transparent material like glass or Perspex.Refraction happens as light enters and leaves a prism. Red light is refracted the least and violet light is refracted the most. This causes the different colours in the light to spread out to form a spectrum. Separating the colours like this is called dispersion. We say that the light has been dispersed.

The colours in the spectrum are red, orange, yellow, green, blue, indigo and violet. It may help to remember them using ROY G BIV or Richard Of York Gave Battle In Vain.Raindrops can disperse sunlight, which is why we see rainbows.

The three primary colours of light are red, green and blue. If all three are mixed together, we get white light.Objects appear white if they can reflect all the colours of the spectrum. Objects appear black if they absorb all the colours of the spectrum.Coloured objects reflect some colours and absorb others. For example, a blue cloth reflects blue light but absorbs the other colours of the spectrum. Shining blue light onto a white object will make the object look blue, as there is only blue light available to be reflected, whereas a black object will still look black in blue light as black objects absorb all light. Shining blue light onto a red object will make it look black as it will only reflect red.Colour filters work by only letting one colour of light through and stopping the other colours.

LIGHT & SOUNDVibration & Sound and

Hearing

What is Sound? Loudness and Amplitude Pitch and Frequency

How We Hear SoundsThe Effect of Loud Sounds

Sound is produced whenever an object vibrates and it transfers energy away from the vibrating object It needs something to travel through - sound cannot travel through a vacuum.Sound travels at different speeds through different substances. In general, the denser the substance, the faster sound travels through it. Sound travels at 5100 m/s through steel, 1480 m/s through water and 330 m/s through air. This is much slower than the speed of light.When an object vibrates, it causes the particles of the substance around it (e.g. air) to vibrate back and forth, which in turn causes the next particles to vibrate and so on, forming a wave. This is how sound travels.Sound can reflect from the surface of an object. This is called an echo. Hard surfaces reflect sound better than soft surfaces.

The loudness of a sound depends upon the amplitude of the vibrations that cause it. Big vibrations transfer more energy than small vibrations, so they are louder.

Sound travels as sound waves. The bigger the vibration, the greater the amplitude of the waves and the louder the sound.

A sound can range from a high to a low pitch. The pitch of a sound depends upon the frequency of the vibrations that cause it. The frequency of a sound is the number of complete waves or vibrations that go past a particular point each second.

Frequency is measured in hertz, with the symbol Hz. 1 Hz is the equivalent of one wave per second.

We hear because sound waves enter the ear and cause the eardrum to vibrate. Three small bones in the inner ear carry these vibrations to the cochlea. The cochlea contains tiny hairs, which send messages to the brain when they vibrate.

We hear a range of sounds from low pitch to high pitch. The range of sound frequencies that we are able to hear is called the audible range. This is roughly between 20 Hz and 20,000 Hz, but d i f ferent people have different audible ranges.

Our hearing is easily damaged and, as we get older, our audible range tends to get smaller. The three small bones may join together as we age, so they are not so good at passing along the vibrations from the ear drum to the cochlea.

Loud sounds, such as those from rock concerts and using personal audio players too loudly, can eventually damage our hearing. If the ear drum is damaged, i t may repair itself again, but if the cochlea is damaged, t h e d a m a g e i s permanent. People with damaged hearing may find it difficult to follow conversations and may need a hearing aid.

ENERGY RESOURCES& ENERGY TRANSFER

Energy Resources

The Variety of Energy Resources

Temperature, Heat and units of Energy

The Ultimate Source of Energy

Generating Electricity

Energy allows things to happen. Energy cannot be created out of thin air or destroyed - it can only be stored or transferred from place to place in different ways.Energy resources provide us with energy. There are different types of energy resource, including fuels such as coal or food, and stores of energy such as batteries or the wind. We can divide energy resources into two categor ies, non-renewable and renewable. Non-Renewable Energy ResourcesNon-renewable energy resources cannot be replaced once they are all used up. Fossil fuels are examples of non-renewable energy resources. The fossil fuels are coal, oil and natural gas. They formed millions of years ago from the remains of living things. Coal was formed from plants, and oil and natural gas from sea creatures. When the living things died, they were gradually buried by layers of rock. The buried remains were put under pressure and chemical reactions heated them up. They gradually changed into the fossil fuels.

Renewable Energy ResourcesRenewable energy resources can be replaced, and will not run out.Examples of renewable energy resources are biomass fuels (fuels from living things such as trees), wind power, water power (wave machines, tidal barrages and hydroelectric power) and solar power.

The energy stored in the fossil fuels originally came from sunlight. Plants used light energy from the Sun for photosynthesis to make their chemicals. This stored chemical energy was transferred to stored chemical energy in animals that ate the plants. When the remains of the plants and animals became fossil fuels, their chemical energy was stored in the fuels. The energy is transferred to the surroundings as thermal energy and light energy when the fuels burn.Just as with the fossil fuels, the energy stored in biomass fuels ultimately came from the Sun.Wind is caused by huge convection currents i n t h e E a r t h ' s atmosphere, driven by heat energy from the Sun.This is why the Sun is regarded as the ultimate source of energy - it provides the energy for all other resources.

Temperature and heat are not the same, although both are concerned with thermal energy. The temperature of an object is to do with how hot or cold it is, measured in degrees Celsius (oC). The heat an object contains is the amount of its thermal energy, measured in joules (J). Joules are the units of Energy.

Most of the UK's electricity is generated in power stations using fossil fuels. Thermal energy released from the burning fuel is used to boil water to make steam, which expands and turns turbines. These drive the generators to produce electricity.As the fossil fuels are non-renewable energy resources, and they produce pollution when they burn, we are aiming to produce more of our electricity using renewable energy resources. This will reduce the rate at which the fossil fuels are used up.

ENERGY RESOURCES& ENERGY TRANSFERConservation of Energy

Forms of Energy and Energy Transfers

Transfer of Heat Energy

Law of Conservation of Energy

Thermal energy can be transferred by:• conduction• convection• radiationThermal energy can also be transferred when a liquid evaporates. The liquid particles with the most energy leave the liquid and enter the surroundings.ConductionThermal energy can move through a substance by conduction. When a substance is heated, its particles gain energy and vibrate more vigorously. The particles bump into nearby particles and make them vibrate more. This passes the thermal energy through the substance by conduction, from the hot end to the cold end.

RadiationAll objects transfer thermal energy by radiation called infrared radiation. The hotter an object is, the more radiation it gives off. No particles are involved in radiation, unlike conduction and convection. This means that thermal energy transfer by radiation can even work in space, but conduction and convection cannot. Radiation is why we can feel the heat of the Sun, even though it is millions of kilometres away in space.

Energy cannot be created out of thin air or destroyed - it can only be stored or transferred from place to place in different ways. This is known as the Law of Conservation of Energy.

Convection The particles in liquids and gases can move from place to place. Convection happens when particles with a lot of thermal energy in a liquid or gas move, and take the place of particles with less thermal energy. Thermal energy is transferred from hot places to cold places by convection.

Energy can take several forms. A vibrating drum or a plucked guitar string transfer energy to the air as sound. This is sound energy. A moving object is said to have kinetic energy (movement energy).

A battery transfers stored chemical energy as electrical energy in the moving charges in the wires. The electrical energy is transferred to the surroundings by a lamp as light energy and thermal energy (heat energy).

A rock on the edge of a mountain has stored energy because of its position above the ground and the pull of gravity. This energy is called gravitational potential energy. As the rock falls to the ground, the gravitational potential energy is transferred as kinetic energy.

When an explosive goes off, chemical energy stored in it is transferred to the surroundings as thermal energy, sound energy and kinetic energy.

Units and Formulae

The following are the important units and formulae you need to know for Common Entrance 13+ exams:

speed = distancetime

QUANTITY UNITS

FORCE Newtons, N

MASS kilograms, kg

TIME seconds, s

WEIGHT Newtons, N

DISTANCE metres, m

AREA square metres, m2 (or cm2)

VOLUME cubic metres, m3 (or cm3)

PRESSURE Pascals, Pa (N/m2) (or N/cm2)

DENSITY kg per m3, kg/m3

SPEED metres per second, m/s

CURRENT Amperes, A

POTENTIAL DIFFERENCE Volts, V

TEMPERATURE degrees Celsius, C

MOMENT Newton-metres, Nm

pressure = forcearea

density = massvolume

moment = force x distance

sd

t PF

A

Dm

V F

M

d

Circuit Symbols