JEE Main 2014 · 6 Apr · Shift 1 · Physics Q12

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PhysicsSingle correct+4 / -1Question 12 of 90

One mole of diatomic ideal gas undergoes a cyclic process ABC as shown in figure. The process BC is adiabatic. The temperatures at A, B and C are 400 K, 800 K and 600 K respectively. Choose the correct statement :

P-V diagram: A (400 K) at lower left; a vertical line rises at constant volume to B (800 K); an adiabatic curve falls from B to C (600 K) at the lower right, at the same pressure as A; a horizontal line returns from C to A.

The change in internal energy in whole cyclic process is 250 R.

The change in internal energy in the process CA is 700 R.

The change in internal energy in the process AB is

-350

The change in internal energy in the process BC is

-500

Answer and worked solution

Official answer: D

For a diatomic gas $\Delta U=\frac52R\Delta T$ (1 mol).

AB: $+400$ K, so $+1000R$ .
BC: $-200$ K, so $-500R$ .
CA: $-200$ K, so $-500R$ .
Whole cycle: 0.

Only (4) is correct.

Topics:First law and internal energy Thermodynamic processes Specific heats of gases

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JEE Main 2014 · 6 Apr · Shift 1, Physics question 12