Charles’ Law

Charle’s  law states that the volume of a given mass of gas is directly proportional to its absolute temperature at constant pressure.

Mathematically,

Volume V        Temperature  T

V    T

V=KT, therefore,  

Where K is a constant

Verification of Charle’s  Law.

The apparatus  shown below is used to verify Charle’s  Law.

Trapped air is heated by passing steam across it . The volume of the gas at any temperature is proportional to the length of the gas. The mercury level is adjusted in the limbs as the temperature increases to maintain the height  on both limbs at the same level. At different temperatures, length of the trapped air is taken while the pressure is maintained at atmospheric by making level a and b to be at the same level . This can be achieved by making mercury at A to drop on a separate container  while heating up the air and by taking the height readings from high temperature to low temperature. In this case the addition of mercury will be needed to maintain the height at the same level when the temperature is coming down to low temperature.

As the temperature increases, trapped air volume increases. As the temperature decreases trapped air volume decreases.

A graph of volume (length ) is plotted against temperature .

A straight line graph is obtained.

Precautions

1. Ensure the air is dry
2. Eliminate air bubbles in the mercury
3. The thermometer must stand upright
4. Take reading when mercury level are stable.

Application of Charle’s Law

1. Absolute zero of temperature
2. The kelvin temperature scales
3. Cubic expansivity of  a gas

Read more about PHYSICS for High Schools