JEE PYQ: Thermodynamics Question 20
Question 20 - 2019 (08 Apr Shift 1)
Which one of the following equations does not correctly represent the first law of thermodynamics for the given processes involving an ideal gas? (Assume non-expansion work is zero)
(1) Cyclic process: $q = -w$
(2) Adiabatic process: $\Delta U = -w$
(3) Isochoric process: $\Delta U = q$
(4) Isothermal process: $q = -w$
Show Answer
Answer: (2)
Solution
From first law of thermodynamics, $\Delta U = q + w$. For adiabatic process, $q = 0$, so $\Delta U = w$ (not $-w$). For isothermal process, $\Delta U = 0$. For cyclic process, $\Delta U = 0$. For isochoric process, $w = 0$.
BETA
