A Levels Physics

A student is studying Brownian motion.
Using a microscope, she observes particles of smoke in a glass container, illuminated by a strong
light. The particles of smoke have a zig-zag path, constantly changing speed and direction.
What happens to the smoke particles if the air in the container is heated?
A The smoke particles become easier to see.
B The smoke particles change direction more frequently.
C The smoke particles increase in volume.
D The smoke particles move further apart.


Choice B is correct because:

When the air in the container is heated, the air molecules gain kinetic energy and move faster. As a result, they collide with the smoke particles more frequently, causing the smoke particles to change direction more often. This increased frequency of collisions leads to the observed increase in the randomness of the Brownian motion.

Choice A is incorrect because:

Heating the air in the container does not directly affect the visibility of the smoke particles. The visibility depends on factors like the size of the particles, the intensity of the light, and the quality of the microscope.

Choice C is incorrect because:

Heating the air in the container does not cause the smoke particles themselves to increase in volume. The changes in motion are due to the increased collisions with air molecules rather than any physical changes to the smoke particles themselves.

Choice D is incorrect because:

Heating the air in the container primarily affects the air molecules' motion and their collisions with the smoke particles. While it is possible that the smoke particles may become slightly more dispersed due to the increased random motion, the primary effect of heating the air is the increased frequency of collisions and changes in direction for the smoke particles.

Phases of Matter | 2014 - O/N - 9702/13 | Q21