Physics UPSC PYQ 2025

Answer the following: Consider a uranium nucleus (₉₂U²³⁶) breaking up spontaneously into two equal parts. Estimate the reduction of electrostatic energy of the nucleus assuming a uniform charge distribution. [Assume the nuclear radius R = 1.2 × 10⁻¹³ A¹∕³ cm] [15M] Is it possible for a photon to transfer all its energy to a free electron? Give reasons. [5M]

Answer the following:

A reversible heat engine operates with three reservoirs at 300 K, 400 K and 1200 K. It absorbs 1200 kJ energy as heat from the reservoir at 1200 K and delivers 400 kJ work. Determine the heat interactions with the other two reservoirs.