A2 Daily A Level Physics question
A 3.0 V head torch originally uses a 0.60 W filament bulb. It is upgraded to a 1.2 W LED module, still powered by the same 3.0 V battery pack. For a continuous 30 min walk, which value is closest to the extra electrical energy taken from the battery by the LED compared with the original bulb?
Answer
The correct answer is C.
Correct: C — 1080 J. The LED uses an extra 0.60 W compared with the bulb; over 30 min = 1800 s this extra energy is 0.60 × 1800 = 1080 J. A is incorrect because 600 J underestimates the time or uses a rounded duration (about 10 min rather than 30 min). B is incorrect because at higher power the device takes more energy per second, so the extra over 30 min cannot be zero. C is correct as it uses the power difference multiplied by time. D is incorrect because 2160 J is the total energy used by the LED alone (1.2 W × 1800 s), not the extra above the original bulb.