Question

Describe an experiment to demonstrate the thermal expansion in a gas.

Answer 1

Take an empty test tube and close its mouth with a single-holed rubber stopper.
Take a capillary tube in which a small amount of coloured water is trapped.
Insert it into the test tube through the single-holed rubber stopper.
Hold the test tube with a test tube holder, and heat it over a burner.
Observe the level of coloured water in the capillary tube.
On heating the test tube, the air in the test tube expands and pushes the coloured water up.
Stop heating the test tube and cool it.
If the test tube is cooled, the air contracts and the level of the coloured water comes down to its original level.
This can also be observed without heating.

• Hold the test tube tightly in your palm.
• The heat from your palm transfers to the air in the test tube.
• The air expands and pushes the coloured water up.
• Hold the test tube between your fingers.
• The air in the test tube cools and contracts.
• The level of the coloured water comes down to its original level.
• This activity confirms that gases expand even when they are exposed to very little heat.
• Thus gases expand on heating and contract on cooling.