Energy - efficiency and power

Question 1

efficiency meaning

Answer 1

the proportion of the energy supplied that is transferred in useful ways.

Question 2

efficiency equation

Answer 2

efficiency = useful energy transferred / total energy supplied (x100 for percentage)

Question 3

how to calculate power

Answer 3

power = work done / time

Question 4

true or false? power = efficiency

Answer 4

true

Question 5

work done equation

Answer 5

work done = force × distance

Question 6

Explain how using more efficient devices reduces the demand for energy

Answer 6

Using more efficient devices reduces the demand for energy because they transfer more of the input energy into useful output and waste less energy, usually as heat or sound. This means that less energy is needed to achieve the same result. When many people use more efficient appliances, the total energy needed across homes and industries is reduced. This lowers the demand on power stations, helps conserve fossil fuels, reduces greenhouse gas emissions, and decreases electricity bills. Therefore, using more efficient devices helps reduce overall energy demand

Question 8

The solar cells on the roof of the house always face in the same direction.
Explain one disadvantage caused by the solar cells only facing in one direction.

Answer 8

fixed solar cells don’t track the Sun so don’t always receive maximum intensity of solar radiation

Question 9

What is the advantage of transmitting electricity at a very high potential difference?

Answer 9

Less thermal energy is transferred to the surroundings.

Question 10

The wasted energy that is not usefully transferred by the solar cells is dissipated.
What happens to energy that has been dissipated?

Answer 10

becomes less useful

Question 11

Why is it unlikely that all the UK’s electricity needs could be met by solar power systems?

Answer 11

A very large area would need to be covered with solar cells.