Question:easy
A gas absorbs \(120\) J of heat and expands by \(300\times 10^{-6} \text{m}^3\) against a constant external pressure of \(2\times 10^5 \text{Nm}^{-2}\). What will be the change in internal energy of the system ?
A gas absorbs \(120\) J of heat and expands by \(300\times 10^{-6} \text{m}^3\) against a constant external pressure of \(2\times 10^5 \text{Nm}^{-2}\). What will be the change in internal energy of the system ?
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Work done by the gas is P times the volume change; then use delta U = q minus w.
Updated On: Oct 1, 2026
- \(180\) J
- \(240\) J
- \(120\) J
- \(60\) J
Show Solution
The Correct Option is D
Solution and Explanation
Step 1: Energy Bookkeeping:
The gas receives 120 J as heat. Some of it leaves again as work pushing the surroundings back, and the rest stays inside as internal energy.
Step 2: Numbers:
Work out $= 2\times10^{5} \times 3\times10^{-4} = 60$ J. The heat left over is $120-60=60$ J.
Step 3: Result:
So $\Delta U = 60$ J, option (D). Adding the work (180 J) would be wrong since the gas does the work.
Final Answer:
Option (D), 60 J. \[ \boxed{\text{(D) } 60\ \text{J}} \]
The gas receives 120 J as heat. Some of it leaves again as work pushing the surroundings back, and the rest stays inside as internal energy.
Step 2: Numbers:
Work out $= 2\times10^{5} \times 3\times10^{-4} = 60$ J. The heat left over is $120-60=60$ J.
Step 3: Result:
So $\Delta U = 60$ J, option (D). Adding the work (180 J) would be wrong since the gas does the work.
Final Answer:
Option (D), 60 J. \[ \boxed{\text{(D) } 60\ \text{J}} \]
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