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 Electrical Heat 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 Electrical 200 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;