What is the cause of this observation of Brownian motion?
The pollen grains absorbing light from the microscope lamp, increasing their kinetic energy.
Convection currents in the water caused by local heating from the light source.
Constant random collisions between water molecules and the pollen grains.
The pollen grains being alive and swimming randomly through the water.
48 exam-style questions on AQA A Level Physics Thermal physics (A-level only), covering Thermal energy transfer (A-level only), Ideal gases (A-level only), and Molecular kinetic theory model (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.