Question

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

Answer 1

Hint:A gas expands on heating. Use this simple fact to think of an experiment. Remember gases cannot be seen directly, hence there must be some indicator to see gases escaping.

Complete answer:
Take an empty flask and a fork with a tiny hole. With the cork, close the mouth of the flask. Now insert a thin capillary tube inside the flask such that the half of the length of the capillary tube is out. Use an iron stand and a clip to hang the flask, inverted, a little above.

Place a glass of water below the flask in such a manner that the capillary tube is dipped inside the water. Note that water doesn’t come inside the flask. Now slowly heat the flask with a burner. You will see small bubbles coming out. However water still doesn’t go inside. This shows that some extra air comes out of the flask when heated.

Thus it proves that gases expand thermally.

Note: All ideal gases follow the ideal gas equation which shows that the volume increases with the increase in temperature. However as the name suggests ideal gases are ideal, they do not exist in the real world. The gases which we know are real gases. The ideal gas equation is modified for real gases and known as real gas equation. But here also real gases expand with increase in temperature. Gases also contract with decrease in temperature. Thus they are directly proportional, provided other parameters are constant.