GCSE Standard Questions: Electricity in the Home

Q4. The table below shows information about different light bulbs.

The bulbs all have the same brightness.

Type of bulb
Input power in watts
Compact fluorescent (CFL)



(i) Calculate the useful power output of the CFL bulb in watts. [2 marks]

(ii) Use your answer to calculate the waste energy in joules produced each second by a CFL bulb. [1 mark]


(i) A growth cabinet is used to investigate the effect of light on the rate of growth of plants.

In the cabinet the factors that affect growth can be controlled. A cooler unit is used to keep the temperature in the cabinet constant. The cooler unit is programmed to operate when the temperature rises above 20 °C.

The growth cabinet is lit using 50 halogen bulbs. Changing from using halogen bulbs to LED bulbs would reduce the cost of running the growth cabinet. Explain why. [4 marks]

(ii) A scientist measured the rate of growth of plants for different intensities of light. Explain what type of graph should be drawn to present the results? [1 mark]

(c) The table below gives further information about both a halogen bulb and an LED bulb.

Type of bulb
Cost to buy
Lifetime in hours
Operating cost over the lifetime of one bulb
2 000
48 000


A householder needs to replace a broken halogen light bulb. Compare the cost efficiency of buying and using halogen bulbs rather than an LED bulb over a time span of 48 000 hours of use.

Your comparison must include calculations. [4 marks]

(Total 12 marks)