A scientific instrument is protected by a sealed flexible air cushion inside a rigid case.
Before the cushion touches the case, it can expand freely and the pressure of the air inside it is equal to the pressure of the surrounding air. Once the cushion touches the case, the case can restrict any further expansion.
At ground level, the volume of the cushion is 6.0 litres6.0\ \text{litres}6.0 litres.
The table gives the conditions at ground level and during a flight in an unpressurised aircraft.
| Location | Air pressure in the compartment / kPa\text{kPa}kPa | Temperature of the cushion / ∘C^\circ\text{C}∘C |
|---|---|---|
| ground level | 100 | 18 |
| during the flight | 45 | -32 |
The cushion first touches the sides of the rigid case when its volume reaches 12.5 litres12.5\ \text{litres}12.5 litres.
The monitoring record uses kelvin for temperatures and temperature changes.
Calculate the two missing values in the monitoring record.
| Quantity | Value |
|---|---|
| temperature during the flight / K\text{K}K | |
| decrease in temperature from ground level / K\text{K}K |
A technician assumes that the temperature of the cushion remains constant at 18 ∘C18\,^{\circ}\text{C}18∘C. The technician also assumes that the rigid case is absent, so the cushion can expand freely during the flight.
Calculate how much the volume that the cushion would occupy at 45 kPa exceeds 12.5 litres12.5\ \text{litres}12.5 litres.
Use the equation
p1×V1=p2×V2p_1 \times V_1=p_2 \times V_2p1×V1=p2×V2
The technician uses the result from (b) to conclude that the cushion will press against the sides of the case during the flight.
Explain why the calculation in (b) is not sufficient to justify this conclusion.
108 exam-style questions on Edexcel GCSE Physics 14.3 Gas pressure and temperature, covering 14.3.1 Gas pressure and particle motion, 14.3.2 Temperature and pressure at constant volume, 14.3.3 Absolute zero and the kelvin scale, 14.3.4 Compressing and expanding gases, 14.3.5 Volume and pressure at constant temperature, and 14.3.6 Doing work on a gas. Each one has a worked solution and a mark scheme showing where the marks go.