Edexcel IGCSE Physics - Energy

Define kinetic energy

The energy an object has as a result of its mass and speed

This means that any object in motion has kinetic energy

Define gravitational potential energy

The energy an object has due to its height in a gravitational field

This means: If an object is lifted up it will gain GPE. If it falls, it will lose GPE

Define elastic potential energy

The energy stored in any compressed or stretched object such as a spring, rubber band, etc.

Define electrostatic energy

Energy due to the force of attraction (or repulsion) between two charges

Define magnetic energy

Energy due to the force of attraction (or repulsion) between two magnets

Define chemical energy

Energy found in fuels, foods or batteries.

This energy is transferred during chemical reactions

Define nuclear energy

Energy stored in the nucleus of an atom

Describe thermal energy

Energy a substance has due to its temperature

In what ways can energy be transferred?

The different energy transfer mechanisms are:

Heating
Electrical
Radiation
Mechanical


Remember HERM!

Describe the energy transfer for a falling object

gravitational potential energy ➝ kinetic energy

Describe the energy transfer for a battery powering a torch

chemical energy ➝ electrical energy ➝ light energy

Describe the energy transfer for a mass on a spring

elastic potential energy ➝ kinetic energy

What is the principle of conservation of energy?

Energy cannot be created or destroyed, it can only be transferred from one store to another


Remember: this means that energy cannot be 'lost', it I just transferred into wasted energy

What are the energy changes in televisions?

Which transfers are useful and which transfers are wasted?

electrical energy ➝ light energy + sound energy + thermal energy

Light and sound energy are useful energy transfers whereas thermal energy (from the heating up of wires) is wasted

What are the energy changes in an electrical heater?

Which transfers are useful and which transfers are wasted?

Electrical energy ➝ thermal energy + sound energy + light energy

Thermal energy is useful, whereas sound and light are not

What are the energy changes in a gas cooker?

Which transfers are useful and which transfers are wasted?

chemical energy ➝ thermal energy + sound energy + light energy

Thermal energy is useful, whereas sound and light are not

What are the energy changes when someone is jumping on a trampoline?

elastic potential energy ➝ kinetic energy ➝ gravitational potential energy

There is also some energy transferred to the surroundings as heat and sound energy

Define efficiency

The ratio of the useful energy transferred by the device to the total energy supplied to the device

(This makes sense when you think of the equation!)

How can efficiency be calculated?

Exam tips:
Efficiency can be a ratio (between 0 and 1) or a percentage.
If the question asks for efficiency as a ratio, give your answer as a fraction or a decimal.

If a system has high efficiency, this means most of the energy transferred is....

Useful

If a system has low efficiency, this means most of the energy transferred is...

Wasted

What are the diagrams that are used to represent energy transfers called?

Sankey diagrams

What do the arrows in a Sankey diagram represent?

The arrow pointing to the right represents useful energy output
The arrow pointing down represents wasted energy

(Remember that the width of each arrow is proportional to the amount of energy going to each store)

How is thermal energy transferred?

By conduction, convection or radiation

Remember that objects will always lose heat until they are in thermal equilibrium (same temperature) with their surroundings, e.g. a mug of hot tea will cool down until it reaches room temperature

What is the main method of thermal energy transfer in solids?

How does it work?

Conduction

When a substance is heated, the atoms vibrate more. As they do so they bump into each other, transferring energy from atom to atom. Metals are especially good at conducting heat as the delocalised electrons can collide with the atoms, helping to transfer the vibrations through the material and hence transfer heat better

Poor conductors are called...

Insulators

What is the main way that heat travels through liquids and gases?

How does this work?

Convection (Remember convection CANNOT occur in solids)

When a fluid (a liquid or a gas) is heated: The molecules push each other apart, making the fluid expand. This makes the hot fluid less dense than the surroundings. The hot fluid rises, and the cooler (surrounding) fluid moves in to take its place. Eventually, the hot fluid cools, contracts and sinks back down againThe resulting motion is called a convection current

Thermal radiation is heat transfer by _______

Infrared

The hotter object, the more infrared radiation it radiates in a given time.

(Remember that all objects, no matter what temperature, emit a spectrum of thermal radiation)

_______ objects are the best at emitting and absorbing thermal radiation

Black

Remember: Black things do not absorb heat (they absorb thermal radiation)

_______ objects are the worst at emitting and absorbing thermal radiation

Shiny

Remember: Shiny things do not reflect heat (they reflect thermal radiation)

What is the only way in which heat can travel through a vacuum? Why?

Radiation

Conduction and convection require particles to transfer heat!

What two factors does the effectiveness of insulation depend on?

How well the insulation conducts heat
How thick the insulation is

How does an insulator keep something warm?

The insulator contains trapped air, which is a poor conductor of heat.
Trapping the air also prevents it from transferring heat by convection.
This reduces the rate of heat loss from the object, meaning that it will stay warmer for longer

The amount of energy transferred (in joules) is equal to the ________ (also in joules)

Work done

Energy transferred (J) = Work done (J)

How can the amount of work done on an object by a force be calculated?

W = f × d

W= work done in Joules (J) or newton-metres (N m)

F = force in Newtons (N)

d = distance in metres (m)

How can the GPE of an object be calculated?

GPE = mgh

GPE = gravitational potential energy, in Joules (J)

m = mass, in kilograms (kg)

g = gravitational field strength in Newtons per kilogram (N/kg)

h = height in metres (m)

What is the gravitational field strength (g) on Earth?

Approximately 10 N/kg

Is the gravitational field strength on the surface of the moon greater than or less than on the earth?

Less than

So it would be easier to lift a mass on the Moon than on the Earth

Is the gravitational field strength on the surface of the gas giants (eg. Jupiter and Saturn) greater than or less than on the earth?

More than

So it would be harder to lift a mass on the gas giants than on the Earth

How can kinetic energy be calculated?

KE = ½ × m × v2

Where: KE = kinetic energy in Joules (J)m = mass of the object in kilograms (kg)v = speed of the object in metres per second (m/s)

How is power defined?

Power is defined as the energy transferred per unit time or the work done per unit time

Exam tip: Think of power as “energy per second”

How is power calculated?

Energy or work done/time

E or W = The energy transferred, or work done, measured in joules (J)

t = time measured in seconds (s)

P = power measured in watts (W)

How is a renewable energy resource defined?

An energy source that is replenished at a faster rate than the rate at which it is being used

As a result of this, renewable energy resources cannot run out

Give examples of renewable energy resources

Solar energy
Wind
Bio-fuel
Hydroelectricity
Geothermal
Tidal

How are fossil fuels used as an energy resource?

Burning fossil fuels produces steam which can turn turbines

Describe the energy transfers that occur in fossil fuels when they are used as an energy resource

chemical energy → thermal energy → kinetic energy → electrical energy

How is nuclear energy used as an energy resource?

Nuclear fuel is reacted, producing heat which creates steam that can turn turbines

Describe the energy transfers that occur when nuclear energy is used as an energy resource

nuclear energy → thermal energy → kinetic energy → electrical energy

How are bio-fuels used as an energy resource?

Plant matter, ethanol or methane can be produced and then burned directly to generate energy

Describe the energy transfers that occur when bio-fuels are used as an energy resource

chemical energy → thermal energy → electrical energy

How is wind used as an energy resource?

Wind turbines can be used to produce electricity

Describe the energy transfers that occur when wind is used as an energy resource

kinetic energy → electrical energy

How is hydroelectric energy used as an energy resource?

Hydroelectric uses the GPE of water stored in reservoirs to turn turbines which generate electricity

Describe the energy transfers that occur when hydroelectricity is used as an energy resource

gravitational potential energy → kinetic energy → electrical energy

How is geothermal energy used as an energy resource?

Heat from underground can be used to create steam which spin turbines, producing electricity

Describe the energy transfers that occur when geothermal energy is used as an energy resource

thermal energy → kinetic energy → electrical energy

How is tidal energy used as an energy resource?

A dam is used to trap seawater at high tide, which can then be released through a turbine generating electricity

Describe the energy transfers that occur when tidal energy is used as an energy resource

kinetic energy → electrical energy

How is solar power used as an energy resource?

Solar cells convert light energy directly into electrical energy, or thermal radiation from the sun is used to warm water passing through black pipes

What is meant by a reliable energy resource?

A reliable energy resource is one that can produce energy at any time

Remember: Non-reliable resources can only produce energy some of the time (e.g. when it’s windy)

Advantages and disadvantages of fossil fuels

Advantages

Reliable

Can produce large amounts of energy at fairly short notice

Disadvantages

Produces significant greenhouse gases and pollution

Advantages and disadvantages of nuclear energy

Advantages

Reliable

Produces no greenhouse gases or pollution

A large amount of energy is produced from a small amount of fuel

Disadvantages

Produces dangerous radioactive waste that can take thousands of years to decay

Advantages and disadvantages of bio-fuels

Advantages

The CO2 produced while burning the fuel is balanced by the CO2 absorbed while producing it

Renewable

Disadvantages

Can take up a lot of land and consume resources that are needed for food production

Advantages and disadvantages of wind energy

Advantages

Renewable

Produces no greenhouse gases or pollution

Land can still be used for farming

Disadvantages

Not reliable - no wind = no electricity

Wind farms are noisy and may spoil the view for people living near them

Advantages and disadvantages of hydroelectric energy

Advantages

Renewable

Reliable

Can produce a large amount of energy at short notice

Produces no pollution or greenhouse gases

Disadvantages

Hydroelectricity dams flood farmland, destroying important wildlife habitats and pushing people from their homes

Advantages and disadvantages of tidal energy

Advantages

Tides are very predictable and a large amount of energy can be produced at regular intervals

Disadvantages

Very few suitable locations. Can destroy the habitat of estuary species

Advantages and disadvantages of geothermal energy

Advantages

Reliable

Renewable

Geothermal power stations are usually small

Disadvantages

Can result in the release of harmful gases from underground

Not many places are suitable

Advantages and disadvantages of solar energy

Advantages

Renewable

No greenhouse gases or pollution

Good for producing energy in remote places

Disadvantages

Not reliable - only work when sunny and do not work at night

Solar farms can use up lots of farmland

Expensive and inefficient