energy resources + energy transfers

Give a description of chemical energy store

Energy stored in chemical bonds

Give a description of the kinetic energy store

energy of a moving object

give a description of the gravitational potential energy store

energy of an object at a height

give a description of the elastic potential energy store

energy stored when an object is stretched or squashed

give a description of the nuclear energy store

energy stored in the nucleus of an atom

give a description of the thermal energy store

total kinetic + potential energy of the particles in an object

give a description of the magnetic energy store

energy stored when repelling poles pushed closer together or attracting poles pulled further apart

give a description of the electrostatic energy store

energy stored when repelling charges pushed closer together or attracting charges pulled furthere apart

how may energy be transferred?

- mechanically
- electrically
- by heating
- by radiation

how may energy be transferred mechanically?

by a force moving an object through a distance

how may energy be transferred electrically?

charges moving due to a potential difference

how may energy be moved through heating

due to temperature difference caused electrically or by chemical radiation

how may energy be moved through radiation?

energy transferred as a wave eg. light and infrared

what is the source of most of the Earth's energy?

the sun
transferred to earth by radiation

define conservation of energy

- Energy cannot be created or destroyed - it can only be converted from one form into another
- Energy input = energy output

Describe the energy changes in an object falling to ground

- Kinetic energy increases
- Gravitational potential energy decreases

Describe the energy changes when a falling object hits the ground

- Kinetic energy decreases
- Wasted energy is thermal and sound energy

How is efficiency calculated?

Efficiency = useful energy output/total energy output x 100

What do Sankey diagrams show?

- How all the energy in a system is transferred into different stores

How may thermal energy transfer take place?

- By conduction, convection and radiation

Describe the process of conduction

- Heat makes the particles vibrate more
- Particles collide with each other and pass their kinetic energy along
- Eventually the thermal energy will be spread through the solid
- Metals are good conductors of heat
- Plastics and air are poor conductors of heat (good insulators)

Why is air a poor conductor of heat?

- Air particles are widely spaced
- Do not collide with each other often

Describe the process of convection

- Heat causes particles to gain kinetic energy
- Particles vibrate and spread out
- Fluid becomes less dense
- Particles rise
- Particles cool and sink setting up a convection current
- Process repeats
- Occurs in fluids (liquids and gases)

Describe how a radiator heats up a cold room

- By convection
- Radiator heats surrounding air
- Heat causes particles to gain kinetic energy
- Particles vibrate and spread out
- Air becomes less dense
- Warm air rises
- Particles cool and sink setting up a convection current
- Process repeats

What is thermal radiation?

Infrared radiation (an electromagnetic wave)

Describe the difference in the radiation absorbed and emitted by dark and light objects

- Dark, matt surfaces are the best absorbers and emitters of radiation
- White, shiny surfaces are the worst absorbers and emitters of radiation
- The hotter the object, the more radiation that occurs

Describe the difference in the radiation reflected by dark and light objects

- White, shiny surfaces are the best reflectors of radiation
- Dark, matt surfaces are the worst reflectors of radiation

How does heat transfer occur in a vacuum?

- By radiation only
- No particles present so conduction and convection cannot occur

Describe how energy is transferred from a stove to food cooking in a pan of water

- Conduction from stove to pan
- Conduction through pan
- Conduction from pan to water
- Convection in the water
- Conduction from water to food
- Conduction through food

How does a vacuum flask prevent heat loss?

- Shiny walls - reflect infrared radiation
- Plastic lid is a good insulator - prevents heat loss by conduction
- Vacuum between walls - prevents heat loss by conduction and convection

How may the rate of energy transfer be reduced at home?

- Loft insulation - fibreglass is a good insulator
- Cavity wall insulation - foam is a good insulator and prevents convection currents being set up
- Aluminium foil behind radiators - reflects infrared radiation back into room
- Double glazed windows - vacuum between glass reduces conduction and convection

What is the equation linking work done, force and distance?

- Work done = force x distance
- W = F x d
- Units = Joules (J)

What is the relationship between work done and energy transferred?

- Work done = energy transferred

Give the equation linking gravitational potential energy, mass, gravitational field strength and height

- Gravitational potential energy = mass x gravitational field strength x height
- GPE = m x g x h

What is the value of gravitational field strength on Earth?

- 9.8 m/s2 (Note: it is fine to use 10 m/s2 if a value is not given in the question)

Give the equation linking kinetic energy, mass and velocity

- kinetic energy = 1/2 x mass x velocity^2
- KE = 0.5 x m x v^2

What is the relationship between gravitational potential energy and kinetic energy?

- Gravitational potential energy lost = kinetic energy gained

Define power

The rate of energy transfer (or rate of doing work)

Give the equation linking power, work done and time taken

- Power = work done/time taken
- P = W/T
- Units = Watts (W)

Describe the energy transfers involved when water from a reservoir is used to generate electricity

- Water has initial gravitational potential energy
- GPE transferred to kinetic energy as water moves
- GPE lost = KE gained
- Work done by water flowing through turbine
- Electrical energy produced