Brownian Motion Experiment
TAP 601-1: Brownian motion
Brownian motion (named after the botanist Robert Brown) is the presumably random drifting of particles suspended in a fluid (a liquid or a gas) or the mathematical model used to describe such random movements, which is often called a particle theory.
The experiment of Brownian motion in a smoke cell is a classic experiment that gives strong circumstantial evidence for the particulate nature of air.
Materials:
✓ Smoke cell, incorporating a light source and lens (Whitley Bay pattern)
✓ Microscope, low power (e.g. x10 objective, x 10 eyepieces) and large aperture
✓ Power supply, 0 to 12 V dc
✓ Microscope cover-slip
✓ Smoke source (e.g. paper drinking straw)
Setting up apparatus:
[pic]
The smoke can come from a piece of burning cord using a dropping pipette or a burning straw (preferably paper). The straw should burn at the top and then be extinguished. The bottom end of the straw should poke into the plastic smoke container.
The cell may need to be cleaned if a waxy or plastic straw is used.
Remove the glass cell from the assembly to clean it. Afterward, push it fully back into the assembly. It may help to wet the outside of the glass tube. You will find it helpful to clean the glass cell after every five to ten fillings to obtain the best results; otherwise the light intensity is reduced.
The cell is illuminated from one side to make the smoke particles visible under the microscope. This is called dark ground illumination. A small piece of black card prevents stray light from the lamp reaching the eye. The lamp is placed below the level of the glass rod in order to minimise convection.
Procedure:
[pic]
1. Fill the cell with smoke using a dropping pipette and cover it with a glass cover-slip. This will reduce the rate of loss of smoke from the cell
2. Place the cell on the microscope stage, fit the mask and
Brownian motion (named after the botanist Robert Brown) is the presumably random drifting of particles suspended in a fluid (a liquid or a gas) or the mathematical model used to describe such random movements, which is often called a particle theory.
The experiment of Brownian motion in a smoke cell is a classic experiment that gives strong circumstantial evidence for the particulate nature of air.
Materials:
✓ Smoke cell, incorporating a light source and lens (Whitley Bay pattern)
✓ Microscope, low power (e.g. x10 objective, x 10 eyepieces) and large aperture
✓ Power supply, 0 to 12 V dc
✓ Microscope cover-slip
✓ Smoke source (e.g. paper drinking straw)
Setting up apparatus:
[pic]
The smoke can come from a piece of burning cord using a dropping pipette or a burning straw (preferably paper). The straw should burn at the top and then be extinguished. The bottom end of the straw should poke into the plastic smoke container.
The cell may need to be cleaned if a waxy or plastic straw is used.
Remove the glass cell from the assembly to clean it. Afterward, push it fully back into the assembly. It may help to wet the outside of the glass tube. You will find it helpful to clean the glass cell after every five to ten fillings to obtain the best results; otherwise the light intensity is reduced.
The cell is illuminated from one side to make the smoke particles visible under the microscope. This is called dark ground illumination. A small piece of black card prevents stray light from the lamp reaching the eye. The lamp is placed below the level of the glass rod in order to minimise convection.
Procedure:
[pic]
1. Fill the cell with smoke using a dropping pipette and cover it with a glass cover-slip. This will reduce the rate of loss of smoke from the cell
2. Place the cell on the microscope stage, fit the mask and