Energy and efficiency Flashcards
The useful energy transfer that happens in an electric lamp is:
Electricity > Light
‘Wasted energy’ becomes less useful because:
It becomes increasingly spread out
Which equation can be used to calculate the efficiency of an energy transfer?
efficiency = useful energy out ÷ total energy in
In a certain device, 25% of the energy is usefully transferred. The energy efficiency of this device is:
25%
A coal-fired power station is 40% efficient. This means that:
40% of the chemical energy stored in coal is transferred to electrical energy
energy = power × time
How much energy is transferred by a 500 W electric drill in 30 seconds?
15,000J
A 250W computer is switched on for 4 hours. How many Units of electricity does it use?
1 K/Wh
A 2 kW electric fire is switched on for 30 minutes. How many Units of electricity does it use?
It would use 1 unit of electricity.
If one Unit of electricity costs 10p, how much will 30 Units cost?
£3
