Energy Transfers Ashfield Direct Learning Madeleine Mantock Ks4 Energy

Energy Transfers

Ashfield Direct Learning

Madeleine Mantock

Ks4 Energy

What are energy transfers?

There are three kinds of thermal energy transfer: conduction, convection and radiation.

The transfer is always from hot to cold.

Radiation

Convection

Conduction

Transfers in Solid, liquids and Gases?

Metals are very good conductors.

Non metals are usually poor conductors (insulators).

Gases are very poor conductors.                                                             

What are energy transfers?

Energy is continually being transferred to and from all objects by radiation, even through empty space (a vacuum).

How energy is transferred When devices transfer

energy, only part of it is usefully transferred

The remainder is transferred in some non-useful way, and therefore is ‘wasted’ or lost to the surroundings

100 joules/sec

ElectricalHeat

Light

80 joules/sec (wasted)

20 joules/sec (useful)

Energy Efficiency

“Efficiency” is the ratio of useful energy to wasted energy

To calculate the efficiency of any device, you need to use the following formula:

Efficiency = Useful energy transferred by device

Total energy supplied to device

Using the efficiency formula calculate the efficiency of this T.V. set

Calculating efficiency

Electrical200 joules/sec

Heat

Light

Sound

150 joules/sec

20 joules/sec

30 joules/sec

Efficiency = 50J x 100% = 25%200J

Remember A T.V. has both light and sound as useful energy transferred.

Hence the calculation is;