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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;