Skip to content
PhysicsNEET 2025First law, work and internal energy

Thermodynamics

Two gases A and B are filled at the same pressure in separate cylinders with movable pistons of radius rAr_A and rBr_B, respectively. On supplying an equal amount of heat to both the systems reversibly under constant pressure, the pistons of gas A and B are displaced by 16 cm and 9 cm, respectively. If the change in their internal energy is the same, then the ratio rArB\dfrac{r_A}{r_B} is equal to:

  1. A.43\dfrac{4}{3}
  2. B.34\dfrac{3}{4}✓
  3. C.23\dfrac{2}{3}
  4. D.32\dfrac{3}{2}

Solution

Same heat, same ΔU\Delta U, so the work done (PΔVP\Delta V) is the same: πrA2×16=πrB2×9⇒rArB=34\pi r_A^2 \times 16 = \pi r_B^2 \times 9 \Rightarrow \frac{r_A}{r_B} = \frac{3}{4}.

Save for spaced revision (free account)

More from this chapter in past papers

From Physics › Thermodynamics › First law, work and internal energy — lectures, notes and every past question on it.

Last revised . Found a mistake? Tell us — corrections are the fastest thing we act on.

ShareWhatsAppTelegram