As In Vanderwall’s gas an internal pressure (P’=a/V^2) developed due to intermolecular attractions.
Therefore Internal work done in Joule’s expansion against internal pressure is :
Due to decrease in internal kinetic energy, the temperature of gas decreases by ΔT and C is heat constant, then decrease in Kinetic energy is :
This is an expression for Joule’s coefficient. I hope you understand this topic, still any query you can write to us in comment box. 😊