IB Physics HL B.3 Gas laws questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceEasy1 mark

A fixed amount of ideal gas changes between the two states shown. The labelled pressures are absolute; $p$ is a positive pressure and $V$ is a positive volume. Which expression gives $T_B/T_A$

Show answer and explanation

Answer: A. For a fixed amount of ideal gas, $PV/T=\text{constant}$ so $T_B/T_A=P_BV_B/(P_AV_A)$ Substituting the values shown gives $(3p)(2V)/[(2p)(V)]=3$ the temperature ratio is dimensionless.
B: reverses the state ratio, giving $T_A/T_B=1/3$
C: omits the volume ratio and uses pressure alone, giving $3/2$
D: omits the pressure ratio and uses volume alone, giving $2$
Remember: compare the products $PV$ when finding temperature ratios for a fixed amount of ideal gas.

Question 2

Paper 2Medium13 marks

A laboratory investigates the pressure exerted by a gas on flat panels. In each trial, a panel forms one wall of a chamber. The outer face of the panel is evacuated, and a sensor measures the force exerted by the gas perpendicular to the panel. The panel area is changed between trials. The measured forces are shown in Figure 1.

(a)

Write the equation defining pressure, P, in terms of force and area, and state what the force represents.

[2]

(b)

Use Figure 1 to determine the pressure represented by the graph, in Pa.

[3]

(c)

A further panel is exposed to gas at the pressure determined in (b). The area of the panel is 0.075 m². Determine the magnitude of the force exerted on the panel.

[2]

(d)

A panel of area 0.12 m² is exposed to gas at the pressure determined in (b). The panel is tilted. Determine the magnitude of the force exerted on it and state the force’s direction relative to the panel.

[3]

(e)

A student concludes that gas pressure increases with panel area because the force shown in Figure 1 increases. Assess this conclusion using the graph.

[3]

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