In a demonstration of Brownian motion, a microscope is used to observe the random motion of tiny smoke particles suspended in air inside a closed cell. Which of the following statements correctly explains how physical conditions affect the observed motion of the smoke particles?
Increasing the temperature of the air increases the average speed of the air molecules, which increases both the frequency of collisions and the average momentum transferred per collision, thereby making the random motion of the smoke particles more rapid.
Using larger, more massive smoke particles increases the total surface area available for collisions, resulting in a more pronounced and violent random motion.
If the air is completely evacuated from the cell to create a vacuum, the smoke particles will exhibit their most rapid motion because there are no longer any air molecules to resist their movement.
The random motion of the smoke particles is primarily caused by collisions between the smoke particles themselves, meaning the speed of the motion increases as more smoke is added to the cell.
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.