Question

The pressure of a gas changes linearly with volume from A to B as shown in figure. If no heat is supplied to or extracted from the gas then change in the internal energy of the gas will be:

Options

• 6 J

• Zero

• −4.5 J

• 4.5 J

Answer 1

4.5 J

Explanation:

|Δ W| = Area under P-V diagram

= `1/2 xx (50 + 10) xx 10^3 xx 150 xx 10^-6`

= `1/2 xx 60 xx 10^3 xx 150 xx 10^-6`

= 30 × 150 × 10⁻³

= 4500 × 10⁻³

4.5 J

As volume is decreasing.

So Δ W = − 4.5 J 

By the first law of thermodynamics.

Δ Q = Δ U + Δ W

0 = Δ U − 4.5

Δ U = 4.5 J