P1 Energy

Energy stores

• magnetic

• internal (thermal)

• chemical

• kinetic

• electrostatic

• elastic potential

• gravitational potential

• nuclear

magnetic energy

The energy stored when repelling poles have been pushed closer together or when attracting poles have been pulled further apart.

magnetic energy - examples

• fridge magnets

• compasses

• maglev trains (use magnetic levitation)

Internal energy

The total kinetic and potential (kinetic) energy in particles in an object.

Internal energy - examples

• human bodies

• hot items

• all items as every item’s particles vibrate - even ice particles vibrate just slower

Chemical energy

Energy stored in chemical bonds, such as those between molecules.

Chemical energy - examples

• foods

• muscles

• electrical cells

Kinetic energy

The energy of a moving object.

Kinetic energy - examples

• runners

• buses

• comets

Electrostatic energy

The energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart.

Electrostatic energy - examples

• thunderclouds

• van de graff generators

elastic potential

The energy stored when an object is stretched or squashed.

Elastic potential - examples

• drawn catapults

• compressed springs

• inflated balloons

Gravitational potential

The energy of an object at height.

Gravitational energy - examples

• aeroplanes

• kits

• mugs on a table

Nuclear energy

The energy stored in the nucleus of an atom.

Nuclear energy - examples

• uranium nuclear power

• nuclear reactors

How long can energy remain in the same store?

sometimes millions and millions of years, or sometimes just for a fraction of a second.

Whenever a system changes…

…there is a change in the way some or all of the energy is stored.

Energy transfers in a boat

Energy transfers in a swinging pirate ship

Energy transfers in a boiling electric kettle

What are the 4 ways energy can be transferred?

• mechanical work

• electrical work

• heating

• radiation

mechanical energy transfer

A force moving an object through a distance

electrical energy transfer

charges moving due to a potential difference

energy transfer by heat

due to temperature difference caused electrically or by chemical reaction

energy transfer by radiation

energy transferred as a wave, eg. light and infrared emitted from the sun

What diagrams are used to show energy transfers?

Sankey Diagrams and transfer diagrams

Sankey diagrams - explanation

Starts off as one arrow that splits into 2 or more points. This shows how all of the energy in a system is transferred. The width of the arrow is drawn to scale to show the amount of energy.

When are Sankey diagrams useful?

When the amounts of energy in each of the energy sources is known.

Transfer diagrams - explanation

• Boxes → show the energy stores

• Arrows → show the energy transfers

dissipated

The spreading out and transfer of energy stores into less useful forms, eg. Causing surroundings to heat up.

Dissipated energy is often referred to as…

‘Wasted’, as it is not transferred to a useful output.

What are examples of dissipated energy? How can this be prevented?

• Electrical cables heating up → wrap wires up in insulator

• When 2 surfaces rub together, increasing their internal energy → add lubricant so less heat lost by friction

• radio/speakers waste energy as infrared radiation

• tumble dryer wastes energy as sound waves

The conservation of energy

Energy cannot be created or destroyed, only tranferred

Example of conservation of energy - skydiver

Skydiver begins to lose gravitational potential energy as he falls out of the plane, but gains kinetic energy as his speed increases. This transfer is mechanical. Some of the energy is dissipated to the air particles as skydiver pushes against them, so they gain internal energy.

Example of conservation of energy - Smartphones

Contain a battery storing chemical energy. When it is in use, electrical work is done and current flows, so the battery’s chemical energy is transferred in many ways (light, sound, …).

Light on screen is emitted as light radiation, and sound waves are produced by speaker vibrating back and forth.

Smartphones also heat up, transferring energy into internal energy which is stored in the atoms of the smartphone’s conductors which emit infrared radiation.

Kinetic energy equation

Elastic potential energy

Gravitational potential energy equation

Work Done Explanation

It is a measure of the energy transfer when a force (F) moves an object through a distance. This means…

energy transferred = work done

…so they are both measured in Joules.

What does the amount of work done depend on?

• The size of the force acting on the object

• The distance through which the force causes the body to move in the direction of a force

Work done equation

force/distance = work done

When work is done on an object…

…energy is transferred.

Power explanation

The rate at which energy is transferred. The more powerful a device is, the more energy it will transfer each second.

Power equation

work done/time = power

1 Watt is equal to…

…1 Joule per second (Power).

What are devices designed to do?

Waste as little energy as possible. As much of the input energy as possible should be transferred into useful energy stores.

Efficieny explanation

How good a device is at transferring energy input into useful energy output.

A very efficient device will…

…waste very little of its input energy.

A very inefficient device will…

…waste most of its input energy.

In other words, what is the efficiency of a device?

The proportion of the energy supplied that is transferred in useful ways. Can be calculated as a decimal or a percentage.

Efficiency equation

Both useful and total energy transfer is measured in Joules.

What is the link between efficiency and power?

Power is equal to the useful energy transferred per second.

Efficiency - alternative equation

Both useful and total power output are measured in Watts.

It is/is not possible to have an efficiency greater than 1 or 100%.

Is not

This would mean that more energy is being transferred than being supplied, which would mean that the energy is being created. This would break the law of conservation.

What are examples of electrical appliances which transfer energy?

• Electric kettle

• Hair dryer

• Light bulb

• TV

Electric kettle - Useful and Wasted energy

• Energy that heats water.

• Internal energy heating kettle and infrared radiation transferred to surroundings.

Hair dryer - Useful and Wasted energy

• Internal energy heating air and kinetic energy of fan blowing the air

• Sound radiation, internal energy heating the hairdryer, infrared radiation transferred to the surroundings.

How is energy transmitted from space to space?

• conduction

• convection

• radiation

Conductor

A material that allows internal (thermal) energy to be transmitted through it easily.

What happens when one end of a metal rod is put into a fire?

The energy from the flame makes the ions in the rod vibrate faster. Since the ions in the solid metal are close together, this increased vibration menas that they collide with neighbouring ions more frequently. Energy is passed on through the metal by these collisions, transmitting energy. More frequent collisions increase the rate of transfer.

Insulator

A material which does not allow the easy flow energy.

Examples of insulators

• cushion on a chair

How can you compare the conductivity of materials?

By examining the time taken to transmit energy through them.

What is an example of comparing conductivities?

Make a fan of rods made of different materials, and heat it at one end with the same flame, whichever rod gets hottest first at the other end is the best conductor, and is said to have thermal conductivity.

Thermal conductivity

A measure of how well a material conducts energy when it is heated.

What are thermal conductivities measured in?

W/m/°C

What is the thermal conductivity of air?

0.024 W/m/°C

Cubic metre

Dimensions 1m x 1m x 1m

How can we insulate homes?

By using materials that are poor conductors - brick, wood, plastic, glass - as energy is not able to be transferred to the home’s surroundings easily.

What are the practicals in this topic?

• Investigating methods of insulation - materials

• Investigating methods of insulation - thickness

• Measuring specific heat capacity

What happens when materials are heated?

The molecules gain kinetic energy and start moving faster. The material gets hotter.

Temperature

A measure of the average kinetic energy of the molecules.

Materials require the same / different amounts of energy to change temperature.

Different

The amount of energy a material needs to change temperature depends on…

• the mass of the material

• the substance of the material (specific heat capacity)

• the desired temperature change

Materials with low/high specific heat capacities will warm up and cool down the fastest. This is because…

Low

This is because it doesn’t take up too much energy to change its temperature.

Specific Heat Capacity

The energy required to raise 1kg of a material by 1°C.

Specific Heat Capacity Equation

mass x SHC x temp change = energy

Specific Latent Heat of Fusion

The energy needed to change the state of 1kg of the substance from a solid to a liquid, at its melting point

Specific Latent Heat of Vapourisation

the energy required to change 1kg of a substance from liquid to gas at its boiling point

Specific Latent Heat Equation

SLH x mass = energy

Specific Heat Capacity of water

4,200

Specific Heat Capacity of brick

840 J/kg°C

energy resources

Systems that can store and supply large amounts of energy.

What are the major energy resources available to produce electricity? (9)

• fossil fuels

• nuclear fuel

• bio-fuel

• wind

• hydroelectricity

• geothermal

• tidal

• water waves

• the sun

Fossil fuels

Natural, finite fuel formed from the remains of living organisms, eg. oil, coal, natural gas.

Nuclear fuel

Radioactive materials, usually uranium or plutonium, used in nuclear reactors.

Hydroelectricity

Electricity generated by the movement of water.

Geothermal

Energy from the heat of the earth.

Where does all the energy on the earth come from?

Ultimately it is from the sun, but it has been stored as different energy resources.

Where is energy needed?

• Homes

• Public service

• Factories and farms

• Transport

Why is energy needed in homes?

for cooking, heating and running appliances

Why is energy needed in public services?

running machinery and warming rooms

examples include schools and hospitals

Why is energy needed for transport?

buses, trains, cars and boats all need a fuel source and some trains and trams connect to an electricity supply

Why might producing and distributing electricity not be good?

Releasing some energy stores can cause damages to the environment by causing pollution and releasing waste products.

What is the effect of burning fossil fuels?

Releases carbon dioxide, adding to the greenhouse effect, and sulphur dioxide which causes acid rain.

What happened during the Industrial Revolution?

Advances in automation and transport caused a significant increase in the amount of fossil held extracted and burnt.

What happened in the 20th century?

electricity used to distribute energy. This powered a range of devices eg. lighting, heating, computing technologies and operating machinery.

How does the demand for energy vary?

Varies with the…

• Time of day

• Time of year