Physics Thermodynamics First Law of Thermodynamics (Delta Q = Delta U + Delta W) Single Correct MCQ
Published on: September 12, 2026

A perfect gas goes from state A to another state B by absorbing $8 \times 10^{5} \mathrm{J}$ of heat and doing $6.5 \times 10^{5} \mathrm{J}$ of external work. It is now transferred between the same two states in another process in which it absorbs $10^{5} J$ of heat. Then in the second process

A
Work done on the gas is $0.5 \times 10^{5}$ J
B
Work done by gas is $0.5 \times 10^{5} \mathrm{J}$
C
Work done on gas is $10^{5}$J
D
Work done by gas is $10^{5}J$

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The correct answer is:
A

In first process using $\Delta Q = \Delta U + \Delta W$

⇒ ⇒ $8 \times 10^{5} = \Delta U + 6.5 \times 10^{5}$ ⇒ ⇒ $\Delta U = 1.5 \times 10J$

Since final and initial states are same in both process

So $\Delta U$ will be same in both process

For second process using $\Delta Q = \Delta U + \Delta W$

⇒ ⇒ $10^{5} = 1.5 \times 10^{5} + \Delta W$ ⇒ ⇒ $\Delta W = -0.5 \times 10^{5} J$

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