A2 Daily A Level Physics question
A sealed steel aerosol can is at 20°C in a lab and later warms to 60°C in direct sunlight. Assume the can’s volume is unchanged and no gas escapes. By roughly what percentage does the internal gas pressure increase?
Answer
The correct answer is B.
Correct: B — Approximately 14% increase. A sealed, fixed-volume gas has pressure proportional to absolute temperature, so from 293 K to 333 K gives 333/293 ≈ 1.14, i.e. about a 14% rise. A uses the Celsius rise as a crude percentage (e.g. 40 out of 100) and ignores that the proportionality uses kelvin. B is correct because converting to kelvin and comparing initial to final temperature gives the proper ratio. C applies a Celsius ratio (60/20) implying a threefold temperature change and hence a 200% pressure rise, which is invalid on the Celsius scale. D divides the temperature change by the final absolute temperature (40/333), giving about 12%, but the fractional change should be relative to the initial state.