Question

In an adiabatic expansion of a gas , its temperature:

Answer 1

In adiabatic expansion of gas the work done (w) in positive as gas expands since in adiabatic process, heat (Q) exchanged is zero, From first law of thermodynamics,

$\Delta u=Q-w$ [$\Delta u$ = change in internal energy]

$\Rightarrow \Delta u=-w$ (as $Q=O$)

Thus for $w>o$, we get $\Delta u<o\Rightarrow$ Internal energy decreases also, $\Delta u=n{C}_{v}T$, where $\Delta T$ = change in temperature.

For $\Delta u<0$ we necessary get $\Delta T<O$

This means, temperature decreases.