Select Page

When a gas expands adiabatically, its volume is doubled while its absolute temperature is decreased by a factor $$1.32$$. Compute the number of degrees of freedom for the gas molecules.

Solution:

The number of degrees can be found from the relation $$f=\frac{2}{\gamma-1}$$
We can find $$\gamma$$ from the adiabatic relation,$$T_2V_2^{\gamma-1}= T_1V_1^{\gamma-1}$$
$$( \frac{V_2}{V_1})^{\gamma-1}=\frac{T_1}{T_2}=1.32$$
$$2^{\gamma-1}=1.32$$
where $$\gamma=1+\frac{log 1.32}{log2}=1.4$$
The number of degrees of freedom $$f=\frac{2}{1.4-1}=5$$