Energy And Efficiency

Question 0

In a certain device, 25% of the energy is usually transferred. The energy efficiency of this device is…

Answer 0

25%

Question 1

Why does wasted energy become less useful

Answer 1

It becomes increasingly spread out

Question 2

A coal-fires power station is 40% efficient. This means that;

Answer 2

40% of the chemical energy stored in coal is transferred to electrical energy

Question 3

Energy = power x time

How much energy is transferred by a 500 W electric drill in 30 seconds?

Answer 3

15,000 J

Question 4

Energy = power x time

A 250 W computer is switched on for 4 hours. How many units of electricity does it use?

Answer 4

250 x 4
=
1000 W
=
1 unit because there are 1000 W in 1 unit

Question 5

Energy = power x time

A 2 kW electric fire is switched on for 30 minutes. How many units of electricity does it use?

Answer 5

1 unit

Question 6

Energy = power x time

If one unit if electricity costs 10p, how much will 30 units cost?

Answer 6

If one unit of electricity costs 10p, 30 units would cost £3