Charles’s Law: At constant pressure, the volume of a fixed mass of gas increases or decreases by 1/273 of its volume at 0°C for every 1°C rise or fall in temperature.

If V₀ is the volume of a gas at 0°C, then its volume at t°C is:

V_t = V₀ \left(1+\frac{\text{t}}{273}\right)

or, V_t = \frac{\text{V₀}(273+\text{t})}{273}

Therefore, \frac{\text{Vₜ}}{273+\text{t}}=\frac{\text{V₀}}{273}

Hence, at constant pressure,

Determination of Absolute Zero

According to Charles’s law,

V_t = V₀ \left(1+\frac{\text{t}}{273}\right)

At absolute zero, the volume of an ideal gas theoretically becomes zero.

Therefore, 0 = V₀ \left(1+\frac{\text{t}}{273}\right)

or, 1 + \frac{\text{t}}{273} = 0

or, t = −273°C

Hence, the value of absolute zero on the Celsius scale is −273°C.