changes in energy

what happens when there’s a change in a system

When there is a change in a system, energy is transferred

how many pathways are there for energy transfer?

4

list the pathways for energy transfer

• Heating by particles 

• Heating by radiation

• Mechanical work done by forces

• Electrical work done when a current flows

describe the energy transfer in heating by particles

Energy transfers by heating increase the energy in the kinetic store of the particles that make up that system, which increases the energy in the thermal store of the object

what are two possible results of energy transfer by heating

• raises the system's temperature

•  produces a change of state (eg. solid to liquid)

describe the energy transfer that takes place when a pan is warming on a hob

Energy is transferred electrically from the mains supply to the thermal store of the hob which is then transferred by heating to the thermal store of the pan

when is mechanical work done?

Mechanical work is done when a force acts over a distance

describe the energy transfer that takes place when a person pushes a box across the floor (system of person and box)

• Energy is transferred mechanically from the kinetic storeof the person to the kinetic store of the box

describe the energy transfer that takes place when a person pushes a box across the floor (system of box and floor) (2)

• If the system is defined as the box and the floor, energy is transferred by heating from the kinetic store of the box to the thermal store of the floor (due to friction

•  by heating to the thermal store of the surroundings as the sound waves transfer energy away from the system and cause the air particles to vibrate

define current

the flow of charge

when does current flow?

A current flows when there is a potential difference applied to the circuit

what is p.d produced by?

This is provided by the power supply or a cell

describe the energy transfer in a circuit (2)

• Energy is transferred electrically from the power supply to the components in the circuit 

  • This is the electrical work done by the power supply when a current flows

describe the energy transfers that take place in a circuit with a lamp and a power supply (3)

• Energy from the chemical store of the cell is transferred electrically to the thermal store of the lamp as the filament heats up

• Energy is transferred from the thermal store of the lamp by heating and by radiation (light) to the thermal store of the surroundings 

• Energy is also transferred by heating to the thermal store of the wires (due to resistance)

what does ‘work done’ mean

Electrical work done means that energy has been transferred when a current flows.