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 |
Efficiency |
Halogen |
40 |
0.15 |
Compact fluorescent (CFL) |
14 |
0.42 |
LED |
7 |
0.85 |
(a)
(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]
(b)
(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 |
Halogen |
£1.50 |
2 000 |
£16.00 |
LED |
£30.00 |
48 000 |
£67.20 |
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)
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