A fire piston is a sealed tube with a tightly fitting piston. A small piece of cotton wool is placed at the closed end of the tube.
The piston is pushed in very quickly. The air in the tube is compressed from 50 cm3 to 2.5 cm3 and the cotton wool catches fire.
The initial pressure of the air is 100 kPa.
Calculate the pressure of the compressed air if its temperature did not change.
Use the equation
P1×V1=P2×V2P_1 \times V_1 = P_2 \times V_2P1×V1=P2×V2
The actual pressure of the compressed air is much higher than your answer to (a).
Explain why.
Explain why the cotton wool does not catch fire if the piston is pushed in slowly.
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.