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GCSE Standard Questions: Electricity in the Home

Q5. The graph shows how the current through a filament lamp changes after the lamp is switched on.

(a) The normal current through the filament lamp is 1.5 A.

Use the graph to determine how long the current through the filament lamp greater than 1.5 A

When a question tell you to 'use the graph' mark your working on it! It is often worth a mark or two! In this question clear use of the graph gets you one mark.

0.08 s

[2 marks]

(b) Why might the filament inside a lamp melt when the lamp is first switched on?

When first switched on the current goes very high (much higher than 1.5 A)The higher the current the more energy is changed into heat energy and the hotter the wire becomes. This can result in the wire melting.

[2 marks]

(c) The lamp is connected to a 24 V power supply.

The current through the lamp is 1.5 A. Calculate the power of the lamp.

P = IV

P = 1.5 x 24

P = 36 W

[3 marks]

(d) LED lamps are much more efficient than filament lamps. Explain what this statement means.

Efficiency is a measure of how much of the energy input is transferred into a useful output. LED lamps change more of the energy input into light energy output than filament lamps do.

[1 mark]

(Total 8 marks)