Energy

What are the energy stores?

-Kinetic

-Thermal

-Chemical

-Gravitational potential

-Elastic Potential

-Electrostatic

-Magnetic

-Nuclear

How can energy be transferred?

-Mechanically

-Electrically

-Through heating via infrared radiation

-Via sound or light waves (radiation)

Define work done

When a force causes an object to move through a distance (causes a displacement) work is done on the object

Work done = energy transferred

What is the principle of conservation of energy?

Energy cannot be created or destroyed, it can only be transferred

What is work done measured in?

Joules, J

Define power

the rate of energy transfer

What is power measured in?

Watts, W

What is meant by kinetic energy?

the energy an object possesses due to its motion, as an object gets faster its kinetic energy increases

What is meant by magnetic energy?

The energy stored when repelling magnetic poles are pushed closer together or when attracting magnetic poles are pushed further apart

What is meant by thermal energy?

-also called internal energy

-all objects have energy in their thermal energy store

-refers to how much energy a substance has, includes two stores of energy - kinetic and potential energy

What is meant by chemical energy?

Energy stored in chemical bonds, e.g those between atoms

Can be released by a chemical reaction

What is meant by gravitational energy?

The energy store of anything with mass in a gravitational field. As an object gets higher its GPE increases

What is meant by electrostatic energy?

Energy stored when repelling charges have been moved closer together or when attracting charges have been moved further apart

Charged objects interacting have energy in their electrostatic energy store

What is meant by elastic potential energy

The energy stored when an object is stretched or compressed

What is meant by nuclear energy?

Energy store that can be released by a nuclear reaction

What happens to the GPE and kinetic energy of a ball as it is thrown in the air?

-If there are no losses (no drag/friction), then the GPE at the highest point is equal to the kinetic energy at the lowest point and vice versa

-change in the store of GPE = change in the store of kinetic energy

Define dissipated energy

energy that is lost to the surroundings

Define open system

one which can gain or lose energy from the ‘outside’ e.g open beaker

Define closed system

one which cannot gain or lose energy from the ‘outside’ e.g enclosed and insulated container

Define waste energy

energy that is not used for its desired purpose

Which type of energy can be transferred by conduction, convection or radiation?

Thermal

What physical state does conduction take place in?

Solid

What physical states does convection take place in?

Fluids - liquid and gaseous states

What is thermal conductivity?

A measure of how well a material conducts thermal energy when heated

How does conduction work?

1. As one end of a solid object is heated, heat energy is transferred to the kinetic energy store of the particles in that end

2. This causes the particles to vibrate faster, so they collide with neighbouring particles more frequently

3. The collisions transfer kinetic energy, meaning the neighbouring particles also vibrate faster - and in turn collide more frequently with their neighbours

4. This process repeats - energy is passed along the object, from one particle to the next

5. Even though it is technically kinetic energy that is transferred, when considering the object as a whole, it is said that it is heat or thermal energy that is transferred

How does convection work?

1. As a fluid is heated, the particles gain kinetic energy, and spread apart

2. This means the heated fluid is less dense, and so it rises above cooler fluid

3. As the fluid cools down it becomes more dense again and so sinks below any warmer fluid

4. If this process occurs in a limited space, such as container or room, it may create a convection current

Describe how heat transfer via radiation works

All objects emit and absorb energy via infrared radiation. Energy can therefore be transferred by one object emitting infrared radiation and another object absorbing it

The hotter an object, the more infrared radiation it will emit

Why will a hot object cool down over time?

A hot object will emit more infrared radiation than it absorbs, therefore it will lose energy (and cool down) over time

When a fluid is heated, does it become more or less dense?

Less dense, as the particles gain energy and spread further apart

What are some methods of reducing heat loss from a home?

-Make walls from a material with low thermal conductivity

-Use cavity walls

-Use double glazed windows - the air gap between the two panes minimise heat loss by conduction. They have a low thermal conductivity, meaning less thermal energy transfers through them

-Insulate walls and attic

What is the purpose of putting insulation in the gap in cavity walls?

To minimise air convection currents

How does the gap in a cavity wall help reduce heat loss?

Heat cannot be conducted across the gap, as the gap contains mostly air which does not conduct heat

Define friction

The resistance that an object encounters when moving over a solid, or moving through a liquid

Can be reduced with a lubricant, such as oil

Define efficiency

A measure of the proportion of energy (or power) that is transferred usefully

For a light bulb what is the useful and wasted energy output?

-Useful: light energy

-Wasted: heat energy

Define a renewable energy resource

One that is being replenished as quickly as it is used

Define a non renewable energy resource

One that isn’t being replenished and so has a limited supply

What is biofuel?

-Fuel made from recently living organisms

-Mostly come from plants or algae, can also use animal waste but less common

What are some examples of renewable energy resources?

-Wind power

-Solar

-Geothermal

-Waves

-Biofuel

-Hydroelectricity

-Tidal power

What are some examples of non renewable energy resources?

-Fossil fuels (coal, crude oil, and natural gas)

-Nuclear energy

Define fossil fuel

A hydrocarbon-containing material, formed naturally in the earth’s crust from the remains of dead plants and animals

What are the advantages of biofuels?

-cheap to make

-easy to transport

-can mix with fossil fuels

-renewable (they absorb the same amount of carbon dioxide while growing as they release when they’re burned)

What are the disadvantages of biofuels?

-need somewhere to grow them

-harvesting, processing, transporting releases carbon dioxide

What are the advantages of coal?

-relatively cheap

-reliable

-easy to mine

-easy to transport

-can produce a lot of energy

What are the disadvantages of coal?

-mining can damage habitats

-produces a lot of carbon dioxide

-releases sulfur dioxide and nitrogen oxides leading to acid rain

What are the advantages of oil?

-Oil power stations + cheap to build

-can be switched on quickly when needed - reliable

What are the disadvantages of oil?

-limited supply

-releases carbon dioxide when burned

-oil spills can lead to great ecological harm

What are the advantages of natural gas?

-cheap

-reliable

What are the disadvantages of natural gas?

-when burned it releases carbon dioxide

-limited supply

-drilling for gas releases methane

What are the advantages of nuclear?

-can provide power with no greenhouse gasses

-pollution free if nothing goes wrong

-reliable

What are the disadvantages of nuclear?

-produces radioactive waste - extremely toxic and can stay toxic for thousands of years

-a lot of money has to be spent on safety - nuclear accident can be a major disaster

Define nuclear energy

it is obtained by nuclear reactions, such as nuclear fission reactions in nuclear power stations

What is geothermal energy?

-the thermal energy generated and stored in the earth

-origins from the original formation of the plant and the radioactive decay of materials like uranium deep inside the earth

How do geothermal power stations work?

-In regions with lots of volcanic activity, the ground is naturally very hot

-If cold water is pumped down into the ground, it will be heated by the hot rocks

-Can directly use the heated water to heat homes

-Can allow the water to heat up so much it turns into steam

-The steam can then be used to turn a turbine, which can drive a generator to produce electricity

Where can geothermal power stations be used?

In areas with lots of heat under the ground, such as volcanic regions

What are the advantages of geothermal?

-relatively cheap once it gets going

-doesn’t release carbon dioxide

-renewable

-no fuel needed

What are the disadvantages of geothermal?

-limited locations: can only do it where there is magma close to the surface

-hard and expensive to set up

-doesn’t produce a lot of energy

How is wind power generated?

By wind turbines, which have blades that spin due to the wind. This spinning action turns a generator which produces electricity

What energy transfer takes place when generating wind power?

As the wind spins the blades, energy from the kinetic energy store of the wind is transferred to the kinetic energy store of the blades. This energy is then converted to electrical energy by the generator

How is solar power generated?

Is generated by solar cells or solar panels, which can generate electricity directly from sunlight

What are the advantages of solar power?

-no emissions of harmful gasses

-won’t run out

-free fuel when set up

What are the disadvantages of solar power?

-only works during the day

-output depends on the weather

-expensive to install

-unreliable

What are the advantages of wind power?

-easy to install

-wind is free

-renewable

-produces no waste or greenhouse gasses

-land beneath can usually still be used for farming

What are the disadvantages of wind power?

-Unpredictable

-Some people feel they are noisy and unsightly

-weather dependant

-can only be installed in some locations

-Need a lot of them to produce an equivalent amount of power toa coal power station

-Requires skilled climbers to repair and maintain wind turbines

How is hydroelectricity generated?

-As water flows downhill, a hydroelectric dam will trap the water in a man made lake

-Whenever water is released through the dam, it spins turbines which are connected to generators, and so produces electricity

-The water can then return to the river on the downstream lower side of the dam

What are the advantages of hydroelectricity?

-very little danger to human or animal life

-flexible - can control the power output

-reliable

What are the disadvantages of hydroelectricity?

-very expensive to build

-can damage habitats and fish cycles while building

-limited places where it can be built

-most usable rivers have been dammed

How do tidal barrages generate electricity?

-as the tide comes in, a tidal barrage will trap the water upstream

-once the tide has gone back out, water is released through the dam which spins turbines connected to generators, and so produces electricity

-the water can then return to the river on the downstream side of the tidal barrage

What are the advantages of tidal power?

-renewable

-doesn’t produce carbon dioxide

-reliable

-can produce electricity when you want

-low environmental impact

-ocean water is 832 times more dense than air so water generates more electricity than air

What are the disadvantages of tidal power?

-can only be planted on coastlines where there is a 5m difference between high and low tide

-tide cycles don’t match consumption patterns

What energy transfer takes place in hydroelectric dams and tidal barrages?

-GPE → kinetic energy →electrical energy

In both cases the water on the higher side contains lots of GPE. This energy is transferred to kinetic energy as the water rushes down to the lower side. As the water moves past turbines, some of its kinetic energy is transferred to the turbines, causing them to start spinning. The generators use this energy to generate electrical power

What is wave power?

The water in the sea rises and falls because of waves on the surface. Wave machines use the kinetic energy of this motion to drive electricity generators

What are the advantages of wave power?

-can be installed at small scale for isolated communities

-no fuel cost

-no harmful emissions

What are the disadvantages of wave power?

-high initial cost

-unreliable

-can only be installed in some locations

-can impact habitats