Momentum is conserved in MCQ with Answer and Explanation

Explanation:
A refrigerator is a heat pump operating in reverse. A compressor squeezes the refrigerant gas, raising its temperature. As it passes through coils on the back (condenser), it releases heat and condenses into a liquid. This liquid expands through a valve, cooling rapidly, and flows into the evaporator coils inside the fridge, where it absorbs heat from the food and evaporates back into a gas.

Explanation:
Optical fibers: TIR confines light in core. Diamonds: high n gives small θ_c, causing multiple TIRs for sparkle. Memory aid: 'TIR applications: fibers (communication), diamonds (optics)'. Optics application frequently tested in competitive exams.

Explanation:
Speed of sound in air v ∝ √T, where T is absolute temperature in Kelvin. T₀ = 0°C = 273 K, v₀ = 332 m/s. T = 27°C = 300 K. Thus v = v₀√(T/T₀) = 332 × √(300/273) ≈ 332 × √1.099 ≈ 332 × 1.048 ≈ 348 m/s ≈ 350 m/s. Approximate rule: speed increases by 0.6 m/s per °C rise, so 27×0.6≈16.2, 332+16.2≈348.2 m/s. Memory aid: 'v ∝ √T in Kelvin'. Such temperature-dependence problems test application of sound wave properties, common in competitive exams with emphasis on absolute temperature usage.