4.1 Energy

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What is a system? What happens when a system changes?

• A system is an object or group of objects

• There are changes in the way energy is stored when a system changes

Describe what an open system is and what a closed system is

• Open systems: able to exchange energy and matter with their surroundings

• Closed systems: unable to exchange energy and matter with their surroundings

  • When there are energy transfers in a closed system, there are no net changes to the total energy

Name all energy stores

My GCSE Kids Hate Learning Energy Names

Potential energy: energy stored in an object or system due to its position, arrangement or state.

• Magnetic energy

  • Energy due to attraction between two magnetic objects

• Gravitational potential

  • The energy an object possesses due to its position in a gravitational field

• Chemical

  • A form of potential energy stored within the structural bonds of atoms and molecules

• Sound

  • Sound energy is the energy carried by vibrations that travel through a medium as a result of oscillating particles

• Elastic potential

  • Energy stored in an object when it is stretched or compressed (its shape has been distorted), provided it does not exceed the limit of proportionality

• Kinetic

  • The energy an object possesses due to its motion

• Heat (thermal)

  • The energy of an object due to the kinetic energy of its atoms and molecules moving or vibrating

• Light

  • A form of energy that is carried by electromagnetic waves

• Electrostatic

  • A potential energy store created by the position of electric charges within an electric field

• Nuclear

  • Energy stored in the nucleus of an atom, released during nuclear reactions (eg. fission, fusion)

State the law of conservation of energy

• Energy cannot be created or destroyed

• only transferred usefully, stored or dissipated

Describe the changes in the way energy is stored when a ball is projected upwards

• When an object is projected upwards, such as a ball, it will initially have kinetic energy (KE).

• As the object rises higher into the air, the kinetic energy will be transferred into gravitational potential energy (GPE).

• Once the object reaches its highest point, the gravitational potential energy will all be converted into kinetic energy as the object falls back to the ground.

Describe the changes in the way energy is stored when a moving object hits an obstacle

• A moving object will start off with kinetic energy.

• Once it hits an obstacle, the kinetic energy can be transferred into many different types of energy:

  • It can be transferred to the surroundings as thermal energy and sound waves.

  • Some of the kinetic energy of the moving object can even be transferred to the kinetic energy store of the obstacle, causing it to move.

Describe the changes in the way energy is stored when a car is accelerating

• As the car moves, the chemical energy store of the petrol will be transferred to the kinetic energy store of the car

• Some of the energy is also transferred to the surroundings by sound waves and the thermal energy store of the surroundings will also increase

Describe the changes in the way energy is stored when a vehicle is slowing down

• As the car slows down, its kinetic energy store will be converted to the thermal energy store of the surroundings and the brakes

• Some of the energy is also transferred by sound waves to the surroundings

Describe the changes in the way energy is stored when bringing water to boil in an electric kettle

• Electric energy from the mains is transferred to the heating element of the kettle which is then transferred to the water by heating, increasing the water’s thermal energy store

• which increases the kinetic energy stores of the particles that make up the water

What are the four main ways (at GCSE level) that energy can be transferred?

• By heating

• Work done when a current flows

• Work done by forces

• By radiation

Formula for kinetic energy of a moving object

kinetic energy = 0.5 x mass x (speed)²

E_k = ½ m v²

E_k - joules, J

m - kilograms, kg

v - metres per second, m/s

Formula for the amount of elastic potential energy stored in a stretched spring

elastic potential energy = 0.5 x spring constant x (extension)²

E_e = ½ k e²

assuming that the limit of proportionality has not been exceeded

E_e - joules, J

k - newtons per metre, N/m

e - metres, m

Formula for the gravitational potential energy of an object raised above ground level

g. p. e. = mass x gravitational field strength x height

E_p = m g h

E_p - joules, J

m - kilograms, kg

g - newtons per kilogram, N/kg

h - metres, m

What equation can be used to calculate the amount of energy stored in or released by a system as its temperature changes

specific heat capacity equation

Give the equation for specific heat capacity

change in thermal energy = mass x specific heat capacity x temperature change

ΔE = m c Δ θ

ΔE - joules, J

m - kilograms, kg

c - joules per kilogram, J/kg°C

Δ θ - °C

What is the specific heat capacity of a substance?

What are its units?

The specific heat capacity of a substance is the energy required to raise the temperature of one kilogram of the substance by 1°C

Units: joules per kilogram, J/kg°C

Define power

Give its formulae

Power is defined as the rate at which energy is transferred or the rate at which work is done

power = energy transferred / time

P = E/ t

P - watts, W

E - joules, J

t - seconds, s

power = work done / time

P = W/ t

P - watts, W

W - joules, J

t - seconds, s

What is 1 watt equal to?

An energy transfer of one joule per second

In all system changes, what always occurs?

• Some energy is always dissipated

• So that it is stored in less useful ways

• The energy is often described to have been ‘wasted’

Explain the ways to reduce unwanted energy transfers

Insulation, lubrication, streamlining

• Insulation: reduces the rate of energy transfer by heating

  • Thick walls with low thermal conductivity

  • Insulated walls (with air gaps, with foam)

  • Loft insulation

  • Double glazed windows (air gap between two sheets of glass to prevent conduction through the windows, as air has a low thermal conductivity)

• Lubrication: lubricants can reduce the frictional forces acting on an object by reducing the friction between objects’ surfaces as they move

  • Oil on a bike chain

• Streamlining: shaping an object to allow fluids to flow more smoothly over it, reducing the surface area directly pushing against the fluid and put under a large frictional force, and thus reducing the overall frictional force on the entire object

  • Aeroplanes with pointed noses

What does it mean if an object has high thermal conductivity?

• High rate of energy transfer by conduction across the material

What is conduction? (in the context of heat transfers)

Conduction is the process where vibrating particles transfer heat energy to the adjacent particles, and the vibrations are passed throughout the material, leading to the spread of heat

Mainly in solids (as particles are packed closely together so can easily transfer vibrations)

• Energy transferred to an object by heating is transferred to the thermal energy store of the object

• This energy is shared across the kinetic energy stores of the particles in the object

• The particles in the part of the object being heated vibrate more and collide with each other; these collisions cause energy to be transferred between particles’ kinetic energy stores

• The process continues throughout the object until the energy is transferred to the other side of the object; it is then usually transferred to the thermal energy store of the surroundings

What is convection? (in the context of heat transfers)

Convection is the transfer of heat in fluids by the movement of the fluid itself, where warmer, less dense fluid rises and cooler, denser fluid sinks, creating a continuous cycle/ current that distributes heat from hot to cold areas

Only in liquids and gases

• Energy is transferred by heating to the thermal energy store of the fluid

• This energy is shared across the kinetic energy store of the fluid’s particles

• The warmer part of the fluid moves faster and the space between individual particles increases; this causes the area to become less dense

• Because the particles are free to move, the warmer and less dense region will rise above denser cooler regions

• If there is a constant heat source, a convection current will be created where the cooler denser air will be heated and the warmer air will cool as it moves further from the source, and the cycle will repeat

• Heat is distributed throughout the fluid via this current

What is radiation? (in the context of heat transfers)

Transfer of thermal energy by electromagnetic waves (mainly infrared)

What is efficiency? Give the formula

Efficiency is a measure of the amount of energy that is usefully transferred from the total energy supplied

efficiency = useful output energy transfer/ total input energy transfer

efficiency = useful power output/ total power input

State ways to increase the efficiency of energy transfers

• Insulation

• Lubrication

• Streamlining

State and describe what renewable energy resources are

Renewable resources are resources that are (or can be) replenished at the same rate that they are consumed

• They will never be used up

• Do less damage to the environment than non-renewable resources

• Don’t provide as much energy

• Not as reliable as non-renewable resources

State and describe what non-renewable energy resources are

Non-renewable resources are resources that cannot be replenished at the same rate that they are consumed

• They will all run out one day

• They do more damage to the environment than renewable resources

• Provide large amounts of energy

• More reliable than renewable resources

State the non-renewable energy resources

• Fossil fuels:

  • Coal

  • Oil

  • Natural gas

• Nuclear fuel

State the renewable energy resources

• Bio-fuel

• Wind

• Hydro-electricity

• Geothermal

• Tidal

• Solar

• Water waves

Give the three main uses of energy resources

Give examples of what types of energy resources are used for this

• Transport

  • Non renewable: petrol and diesel use fuel created from oil, coal is used in steam trains (to boil water to produce steam)

  • Renewable: run on bio-fuels or a mixture of bio-fuels and petrol or diesel

• Electricity generation

  • Non renewable: coal, natural gas, oil (these fuels are burnt to heat water to produce steam which will turn turbines connected to generators)

  • Renewable: solar panels, wind turbines

• Heating

  • Non renewable: burning natural gas to heat water, coal, electric heaters (using electricity generated from non-renewable sources)

  • Renewable: geothermal heat pump, solar water heaters, burning bio-fuel, electric heaters (using electricity generated from renewable resources)

Describe and explain the trends in energy usage

• During the industrial revolution (18th and 19th centuries), fossil fuels became an important source of energy as it was easy to mine and provided large amounts of energy

• During the 20th century as population grew, electricity use increased

• Since the 21st century, electricity use in the UK has been decreasing as appliances become more efficient and people are consciously trying to use less energy

  • Most of our electricity is produced using fossil fuels and nuclear power

• Throughout the 21st century as technology has developed, it has been more possible to use renewable energy resources; as of the present we are currently trying to move towards renewable energy resources

Describe the environmental impact arising from the use of different energy resources

• Burning fossil fuels releases greenhouse gases into the atmosphere that contribute to the enhanced greenhouse effect; this contributes to global warming

• Burning fossil fuels can also produce sulfur dioxide, which causes acid rain (SO₂ gas released mixes with rain and produces acid rain); this can damage buildings, kill fish in lakes and be harmful to trees and plants

• Coal mining can destroy landscapes and damage habitats

• As oil is extracted, oil spills can occur which affect mammals and birds that live in and around the sea

• When nuclear fuels are used, radioactive waste is produced which is very dangerous and difficult to dispose of

Describe bio-fuel energy resources, give the pros and cons

Bio-fuels are renewable energy resources created from recently living organisms (eg. plants, algae, animal waste)

• They are burned to release energy for transport or to generate electricity; they release carbon dioxide when burnt but are carbon neutral

Pros:

• Renewable resource

• Carbon neutral

• Relatively cheap to produce

• Fairly reliable as crops take a short time to grow

• Can be mixed with fossil fuels for transport (new cars don’t have to be produced/ bought)

Cons:

• Crops need spaces to grow, so large areas of forest are cut down which destroys habitats and releases CO₂ into the atmosphere

• Harvesting, processing and transporting the fuels require large amounts of energy

• Cannot respond to immediate energy demands

Describe wind energy resources; give the pros and cons

Wind energy involves placing wind turbines in exposed areas (eg. moors, coasts); each turbine has a generator inside of it and as the blades spin, they turn the generator, which converts the kinetic energy from the movement to electrical energy, which can then be transported to the national grid

Pros:

• Renewable

• Low running costs

• Once manufactured, no pollutants are produced

• No permanent damage to the landscape if removed

• Don’t damage the environment

Cons:

• High initial costs

• Manufacturing produces pollutants

• Dependent on the weather (unreliable)

• Takes up large amounts of space

• Ugly and noisy

• Impossible to increase energy supply if there’s increased demand

Describe hydro-electricity, tidal and water wave energy resources; give the pros and cons

Hydro-electricity power plants require flooding a valley by building a large dam; water is trapped from upstream. The stored water has large amounts of gravitational potential energy.

Tidal energy is harvested using tidal barrages; large dams are built across river estuaries (where river meets the sea (tides)) with turbines in them.

Water wave energy is harvested using lots of small, wave-powered turbines located around the coast

• The force of the water when released from the dams turn turbines which are connected to generators which convert kinetic energy to electrical energy

Hydroelectric pros:

• Generates very large amounts of energy

• Doesn’t produce pollutants

• Low running costs

• Reliable

• Can provide an immediate response to an increased demand for electricity

Hydroelectric cons:

• Stop boats and fish from travelling through

• Initial set up is very expensive

• Has to flood large areas, which is unsightly and can lead to loss of habitat

Tidal + water wave pros:

• Doesn’t produce pollutants

• Low running costs

• Can be used on large or small scales (tidal resources only)

Tidal + water wave cons:

• Hazardous for boats

• Initial set up is very expensive

• Disturbs the seabed and habitats for marine animals

• Unsightly

• Unreliable as waves may die out when wind drops

Describe solar energy resources; give the pros and cons

Solar cells generate electric currents directly from sunlight

Pros:

• Once running, doesn’t produce any pollutants

• Minimal running costs

• Don’t damage the environment

Cons:

• Solar cells have a low efficiency, and thus a low useful power output

  • Unlikely to be able to generate all electricity for the UK as a really large area of land would need to be covered by solar cells

• High initial costs

• Making them produces pollutants

• Dependent on the weather, unreliable

• No way to increase supply when increased energy demand

• Take up large amounts of space, unsightly

Describe geothermal energy resources; give the pros and cons

Geothermal energy is energy created and stored in the Earth’s crust; the heat originated from the original formation of the planet and from the ongoing radioactive decay in the Earth’s core. Can be used to generate electricity (pump water underground, water is heated into steam which will turn turbines to generate electricity) or to directly heat buildings (water is pumped underground, heated and then pumped through buildings).

Pros:

• Does very little damage to the environment

• Doesn’t produce pollutants

• Renewable

• Reliable

Cons:

• Can only use in certain areas (volcanic activity)

• Power plants are expensive to build, and may produce pollutants during manufacturing

What is the difference between tidal energy resources and water wave energy resources

• Tides are produced by the gravitational pull of the Sun and the moon

• Water waves are produced by the wind blowing across the surface of the ocean

Although we know about the environmental impacts of non-renewable energy resources, why can we not always combat these issues?

• Political

  • Some governments may be reluctant to invest as they want to spend government funding on other things/ don’t want to raise taxes to afford the high cost of renewable resources

• Social

  • People may not want renewable energy resources due to noise and visual pollution

  • Making personal changes can be inconvenient and expensive

• Economic

  • Very expensive start up costs, which governments may be unable to afford/ reluctant to invest in

• Ethical

  • It may be argued to be unethical to use nuclear energy due to the production of nuclear waste, which future generations will have to deal with

  • It may be unethical to raise taxes when many people cannot afford it and do not want their money to go towards renewable energy resources

Give the environmental advantages of using a gas-fired power station to generate electricity compared with using a coal-fired power station

Gas vs coal

• No sulfur dioxide released

  • Doesn’t cause acid rain

• No particulates released (soot)

  • Doesn’t cause global dimming

• Less carbon dioxide released (per kg of fuel)

  • Less global warming

• Gas produces no solid waste, whereas coal produces significant amounts

• Gas mining is less destructive than coal mining (in terms of water contamination and deforestation)

At the bottom of the slide, all riders and their sleds have approximately the same speed. Explain why. (4 marks)

The speed of the riders depends on their kinetic energy, which depends on their inital gravitational potential energy as their E_p will be converted to E_k.

Therefore, E_p = E_k

So, ½ mv² = mgh

v² = gh

Therefore velocity (speed) depends only on gravitational field strength and height (which they all have the same of)

Variations will be due to differences in air resistance, friction or initial speed.

Explain the environmental effects of generating electricity using fossil fuels

releases carbon dioxide which causes global warming

OR releases particulates which causes global dimming or which causes breathing problems

OR releases sulfur dioxide which causes acid rain

OR releases nitrogen oxides which causes breathing problems// which causes acid rain

It is unlikely that all of the electricity that the UK needs can be generated by solar power systems. Explain why.

• a really large area of land would need to be covered with solar cells

• due to the low useful power output of the solar cells

Explain why people should be encouraged to use energy efficient electrical devices.

More efficient devices require a lower energy input for the same energy output, so they waste less energy

which would minimise the energy demand

which would minimise the environmental impact from fossil fuel electricity generation

Girl ran up stairs

Calculating power output using GPE

Total power output was greater than answer. Give reasons why

• Increases kinetic energy as well as gravitational potential

• Some energy is wasted in her muscles

• Some energy transferred as thermal energy to surroundings// some energy transferred due to work done against air resistance

A solar power system is installed in the remote village in addition to the hydroelectric generator. Explain why this improves the reliability of the electricity supply to the village.

(In Summer there is no hydroelectric energy produced)

(Solar system installed in Summer)

• in the summer the power output from the hydroelectric generator is lower but the solar power output would be greater

• so less variation in total power output (which improves the reliability of the supply)

What is meant by the reliability of a power supply?

How does a supply become more consistent

• How consistently

• How dependably

Can provide electricity when needed; doesn’t frequently fail, can meet at all times, is stable and predictable

A supply becomes more consistent if there is less variation in total power output

Explain how the internal energy of a substance changes as it goes from liquid to gas

• Potential energy increases

• But the kinetic energy of the particles does not change

  • As temperature does not change

• So internal energy increases