A cylinder containing a fixed mass of air is sealed with a gas-tight, frictionless piston. The piston is slowly pulled outwards, increasing the volume of the trapped air. The temperature of the air is kept constant. How does the air pressure in the cylinder change and why?
Pressure increases because the air molecules move more quickly.
Pressure increases because the air molecules strike the walls more frequently.
Pressure decreases because the air molecules move more slowly.
Pressure decreases because the air molecules strike the walls less frequently.
321 exam-style questions on CIE IGCSE Physics 2.1 Kinetic particle model of matter, covering 2.1.1 States of matter and changes of state, 2.1.2a Particle structure and motion in solids, liquids and gases, 2.1.2b Gas pressure and particle collisions, 2.1.2c Brownian motion, 2.1.3a The absolute scale of temperature, and 2.1.3b Pressure, volume and temperature of a gas. Each one has a worked solution and a mark scheme showing where the marks go.