JEE Main 2026 Physics question
One mole of diatomic gas having rotational modes only is kept in a cylinder with a piston system. The cross-section area of the cylinder is 4 cm². The gas is heated slowly to raise the temperature by 1.2 °C during which the piston moves by 25 mm. The amount of heat supplied to the gas is J. (Atmospheric pressure = 100 kPa, R = 8.3 J/mol·K) (Neglect mass of the piston)
Answer: (B)
Solution
The gas is heated at the constant (atmospheric) pressure. With translational and rotational modes only, =5R/2, so ΔU=1×2.5×8.3×1.2=24.9 J. Work done=PΔV=100×10³×4×10⁻⁴×25×10⁻³=1 J. Q=ΔU+W≈25.9 J;
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