Efficiency

Question 1

What happens to energy when it’s transferred?

Answer 1

Some energy is dissipated into the thermal energy store of the surroundings. This is called wasted energy.

Question 2

What is efficiency?

Answer 2

• 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

Question 3

State the equation for efficiency

Answer 3

Efficiency = useful output energy transfer ÷ total input energy transfer
(No unit) (Joules) (Joules)

Question 4

24kJ of energy is transferred to a hair dryer. The hairdryer is 45% efficient. How much energy is wasted as sound?

Answer 4

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