A gas does 4.5 J of external work during adiabatic expansion. If its temperature falls by 2 K, then its internal energy will be

Options

A. increased by 4.5 J
B. decreased by 4.5 J
C. decreased by 2.25 J
D. increased by 9.0 J

Answer

B

Explanation

During adiabatic process, no heat transfer takes place,
So, dQ=0
From first law of thermodynamics,
dQ=dU+dW
`Rightarrow dU=-dW`
`Rightarrow dU=-4.5J`
As, the temperature falls so internal energy will decrease i.e. dU=-4.5 J