A Level · A2 · multiple choice
A Level extension · Question 2
A Level extension · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 1
- Topics
- 1
- Answer
- Complete
multiple choice1 mark
An ideal gas is at a thermodynamic temperature of 300 K. To what temperature must it be raised to double the root-mean-square speed of its molecules?
- A
424 K
- B
600 K
- C
1200 K
- D
2400 K
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Answer overviewCorrect answer: C — 1200 K
01
1 markAnswer and reasoning
How to approach it
Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.
- 1
The correct choice is C: 1200 K
- 2
B doubles the temperature, which doubles the mean kinetic energy but multiplies the r.m.s. speed by only √2 — and A is that √2 factor applied to the temperature instead. Since ½m⟨c²⟩ ∝ T, the speed goes as √T, so doubling the speed needs four times the temperature.
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