Electrical power
3 marks · NormalSome light bulbs get hot in normal use. A student wants to design a test to compare the heating effect of two bulbs with different resistances.
State one control variable needed for a fair test.
Suggest a measurement the student could take to compare the heating effect.
Explain the expected result if one bulb has a higher resistance than the other.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Supply voltage (or current, or time bulbs are switched on). · must show One relevant control variable stated
(b) Measure temperature increase (or rate/amount of heat produced) for each bulb. · must show One suitable measurement
(c) The bulb with higher resistance will get hotter as more electrical energy is transferred to heat in a given time, if the current or voltage is kept constant. · must show Correctly links resistance to heating with reason
Common mistakes: Confusing power and resistance
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States relevant control variable.
B2 (b) · 1 mark · Names a sensible measurement to compare heating.
B3 (c) · 1 mark · Explains link between higher resistance and greater heating.
Worked solution
(a) The supply voltage should be kept constant.
(b) Measure the temperature increase of each bulb or the surrounding air.
(c) The higher resistance bulb converts more electrical energy into heat (if voltage or current is constant), so it will get hotter.