ELECTRICAL POWER
3 marks · NormalTwo halogen bulbs are labelled 50 W and 70 W. Both are in use for 20 seconds. The bulbs convert electrical energy into heat and light.
| Bulb | Power (W) | Time (s) | Energy (J) |
|---|---|---|---|
| A | 50 | 20 | |
| B | 70 | 20 |
Calculate the energy transferred by bulb A in 20 seconds.
Calculate the energy transferred by bulb B in 20 seconds.
Explain why bulb B is brighter than bulb A.
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.
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(a) 1000 J
(b) 1400 J
(c) It transfers more energy every second (has a higher power rating). · must show more energy per second, higher power
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correct calculation for energy: 50 × 20 = 1000 J.
M2 (b) · 1 mark · Correct calculation for energy: 70 × 20 = 1400 J.
B1 (c) · 1 mark · Relate higher power to increased brightness (valid comparison).
Worked solution
a) Bulb A energy: E = P × t = 50 W × 20 s = 1000 J.
b) Bulb B energy: E = 70 W × 20 s = 1400 J.
c) Bulb B is brighter because it transfers more energy every second—it has a higher power rating.