Topic Menu

Cyber-chess a chess instruction site

GCSE Questions: Energy Sources

Q21. Here is a hydroelectric power station.

(a) Electricity is generated when water from the reservoir flows through the turbines.

(i) Write down the equation which links density (ρ), mass (m) and volume (V).

density = mass / volume

ρ = m/V

[1 mark]

(ii) The reservoir stores 6,500,000 m3 of water.

The density of the water is 998 kg/m3 .

Calculate the mass of water in the reservoir. (Give your answer in standard form).

ρ = m/V

m = ρV

m = 998 x 6,500,000

m = 648,700,000

m = 6.487 x 108 kg

[4 marks]

(iii) Write down the equation which links energy transferred (E), power (P) and time (t).

energy transferred = power × time

E = Pt

[1 mark]

(iv) The electrical generators can provide 1.5 × 109 W of power for a maximum of 5 hours.

Calculate the maximum energy that can be transferred by the electrical generators.

E = Pt

t = 5 x 60 x 60 s = 18 000 s

E = 1.5 x 109 x 18,000

E = 2.7 x 1013J

[3 marks]

(b) The graph below shows how the UK demand for electricity increases and decreases during one day.

The hydroelectric power station in the diagram above can provide 1.5 × 109 W of power for a maximum of 5 hours.

Give two reasons why this hydroelectric power station is not able to meet the increase in demand shown between 04:00 and 16:00 in this graph.

The variation in demand is much greater than 1.5 × 109 W and demand remains high for longer than 5 hours.

[2 marks]

(Total 11 marks)