1
Q
What happens to energy when it’s transferred?
A
Some energy is dissipated into the thermal energy store of the surroundings. This is called wasted energy.
2
Q
What is efficiency?
A
- Efficiency is a measure of how much energy is transferred to a useful energy store
- Devices that transfer more energy usefully are more efficient than devices that waste more energy
3
Q
State the equation for efficiency
A
Efficiency = useful output energy transfer ÷ total input energy transfer
(No unit) (Joules) (Joules)
4
Q
24kJ of energy is transferred to a hair dryer. The hairdryer is 45% efficient. How much energy is wasted as sound?
A
E Efficiency = useful output energy transfer ÷ total input energy transfer
U 24kJ= 24000J 45%=0.45
S 0.45= uoet ÷ 24000
A useful energy output = 0.45 x 24000= 10800J
C 24000-10800=13200J= 13.2kJ
