Topic Menu

Cyber-chess a chess instruction site

GCSE Standard Questions: Electricity in the Home

Q13. Light bulbs are labelled with a power input and operating voltage.

(a) Tick the one statement that describes what 'power input' means:

The charge transferred each second by the bulb.
  
The current through the bulb.
 
The energy transferred each second to the bulb.
The potential difference across the bulb.
  

 

[1 mark]

(b) Write down the equation which links current, potential difference and power.

P = IV

[1 mark]

(c) A light bulb has a power input of 40 W. The mains potential difference is 230 V. Calculate the current in the light bulb.

I = P/V

I = 40/230

I = 0.17 A

[3 marks]

(d) The table below shows information about three different light bulbs.

Light bulb
Total power input in watts
Useful power output in watts
Efficiency
P
6.0
5.4
0.90
Q
40
2.0
0.05
R
9.0
X
0.30

 

(i) Write down the equation which links efficiency, total power input and useful power output.

efficiency = useful power output/total power input

[1 mark]

(ii) Calculate the value of X in the table.

X/9.0 = 0.30

X = 2.7 W

[3 marks]

(e) In addition to power input, light bulbs should also be labelled with the rate at which they emit visible light. Suggest why.

Bulbs also transfer thermal energy as well as light energy so the efficiency of the light bulb should be given so the consumer knows how much of the energy input actually produces light energy.

[2 marks]

(Total 11 marks)