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IGCSE · 2 · multiple choice

Thermal physics · Question 2

Thermal physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.

Demand
routine
Marks
1
Topics
1
Answer
Complete
A fixed mass of gas trapped in a cylinder, before and after compressionbefore compression300 cm³gaspistonpressure 1.0 × 10⁵ Paafter compression120 cm³pressure = ?the temperature of the gas does not change
Fig. 2.1Two horizontal cylinders are drawn one above the other, each closed at the left-hand end and fitted with a piston on a rod that comes out through the open right-hand end. In the upper cylinder, labelled before compression, the trapped gas fills a column marked 300 cm³ and the pressure beside it is given as 1.0 × 10⁵ Pa. In the lower cylinder, labelled after compression, the piston has been pushed further in so that the gas column is marked 120 cm³, and the pressure beside it is left as a question mark. A note below states that the temperature of the gas does not change.
multiple choice1 mark

A fixed mass of gas has a volume of 300 cm³ at a pressure of 1.0 × 10⁵ Pa. The gas is compressed to a volume of 120 cm³ at constant temperature. What is the new pressure?

  1. A

    0.40 × 10⁵ Pa

  2. B

    1.2 × 10⁵ Pa

  3. C

    2.5 × 10⁵ Pa

  4. D

    3.6 × 10⁵ Pa

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Answer overviewCorrect answer: C — 2.5 × 10⁵ Pa
01

Answer and reasoning

1 mark
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. 1

    The correct choice is C: 2.5 × 10⁵ Pa

  2. 2

    A applies the ratio the wrong way round — the answer must be larger, because squeezing a gas raises its pressure. D multiplies the volumes instead of taking their ratio.

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