Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Brownian motion is defined as the random, erratic, zig-zag movement of microscopic particles suspended in a fluid (liquid or gas).
It is caused by the continuous, random bombardment of these visible particles by the much smaller, invisible, and fast-moving molecules of the fluid.
This phenomenon provides direct evidence for the Kinetic Molecular Theory of Matter, which states that all matter is made of tiny particles in constant motion.
The motion is non-directional because the collisions from the fluid molecules occur at random intervals and from all directions.
The intensity of Brownian motion increases with an increase in temperature, as the fluid molecules gain more kinetic energy () and move faster.
Smaller suspended particles exhibit more vigorous Brownian motion than larger particles because the unbalanced forces have a greater effect on a smaller mass ().
📐Formulae
💡Examples
Problem 1:
During a smoke cell experiment, a student observes bright specks of light moving randomly under a microscope. Identify what these specks are and explain why they move in a zig-zag path.
Solution:
The bright specks are smoke particles reflecting light. They move in a zig-zag path because they are being struck by invisible air molecules moving at high speeds from different directions.
Explanation:
Even though air molecules are too small to see, their collisions with the smoke particles exert a net force () that causes the observable smoke particles to change direction constantly.
Problem 2:
How would the Brownian motion of pollen grains in water change if the water was heated from to ?
Solution:
The Brownian motion would become more rapid and vigorous.
Explanation:
Increasing the temperature increases the average kinetic energy () of the water molecules. This results in more frequent and more forceful collisions with the pollen grains, leading to faster random movement.