Supply and demand

3 marks · Normal

The demand for electricity changes at different times of day.

(a)

State one time of day when electricity demand is likely to be at its highest and explain why.

[1 mark]

(b)

Name a type of power station that responds quickly to sudden increases in electricity demand. Explain why it can do this.

[2 marks]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

(a) Early morning or evening (after work/school), when many people use lights, heating or cooking appliances · must show clear time of day and linked explanation

(b) Gas-fired or hydroelectric power station; they can respond quickly because they can be switched on/off rapidly or release stored water almost instantly. · must show correct station and reason

Common mistakes: Naming slow-responding power stations; describing daily use without an explanation

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · States a correct peak time and links explanation (e.g. morning/evening linked to use of lights/heating/cooking)

B1 (b) · 1 mark · Names a quick-responding station (gas-fired or hydroelectric)

B1 (b) · 1 mark · Gives a reason why it can respond quickly (e.g. turbines started rapidly, water released quickly)

Worked solution

a) Demand is highest in the early evening when people return home and switch on lights, heating and appliances.

b) Gas-fired or hydroelectric stations can respond quickly to sudden increases because gas turbines can be brought online rapidly, and hydroelectric stations can release water instantly to generate power.