Experiment 2.1: Linear expansion of Solids

Linear expansion of Solids

The increase in the length of a body resulting from being heated is known as “linear expansion”, the increase in area is known as “area (superficial) expansion”. And the increase in volume as “cubical expansion”

Generally, when heat is supplied to a body, the body increases in size. This increase in size occurs in all directions and is known as “expansion”. It can therefore be said that a body undergoes thermal expansion when it is supplied with heat energy. On contrary, when cooled, the body contracts. If the changes are resisted, large forces are created which are sometimes useful but at other times are nuisance. According to the kinetic theory the molecules of solids and liquids are in constant vibration. When heated they vibrate faster and force each other a little farther apart. Expansion results and this is greater for liquids.

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Experiment 2.1: Linear expansion experiment

Aim: To demonstrate linear expansion

Method one:

Apparatus: metal bar, metal gauge, Bunsen burner.

A metal bar fits exactly into the gap of a metal gauge when both are at room temperature. The bar and the metal gauge are both shown in the figure below

Bar and gauge apparatus for Linear Expansion Experiment

Separated the bar from the gauge and then heat it strongly for a short while and return it to the gauge.

Observation: You will find that it will not fit into the gauge as it did before. This is because the metal bar has undergone linear expansion.

Method two:

Apparatus: linear expansion apparatus, metal bar, metal rod, Bunsen burner.

Procedure:

The apparatus is arranged as shown in the figure below and the scale pointer is adjusted to zero by pushing or pulling the free end of the metal rod. The screw is then tightened to hold the rod firmly in position as shown in the following figure

Apparatus used to measure linear expansion

Observations: When the metal rod is heated, the pointer moves slowly to the right. The movement of the pointer is caused by the linear expansion of the rod. The amount by which the metal rod actually expands is very small, but the movement of the pointer magnifies the expansion of the metal rod so that it can be seen a little more easily.