Sample 1Medium
On a P-V diagram (V in m³ on the x-axis, P in Pa on the y-axis) a gas is taken round a rectangle with corners at (1 × 10⁻³, 1 × 10⁵), (1 × 10⁻³, 3 × 10⁵), (3 × 10⁻³, 3 × 10⁵) and (3 × 10⁻³, 1 × 10⁵), traversed clockwise. How much heat does the gas absorb in one cycle?
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The answer is D.
In a cycle ΔU = 0, so Q = W. The net work equals the enclosed area, (2 × 10⁵ Pa)(2 × 10⁻³ m³) = 400 J, positive for a clockwise cycle. So 400 J of heat is absorbed.
- A.
The internal energy change is zero, but net work is done, so net heat is not zero.
- B.
200 J is half the enclosed area of 400 J.
- C.
600 J is the work done in the expansion at 3 × 10⁵ Pa alone, without subtracting the work done on the gas in the compression.
NCERT: Class 11 Physics, Chapter 11