Photoelectric emission requires: MCQ with Answer and Explanation

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.

Explanation:
Telescope (refracting/reflecting) makes distant objects appear nearer, magnified. Microscope for tiny near objects. Periscope uses mirrors to see over obstacles. Endoscope medical.

Explanation:
η = 1 - 300/600 = 1 - 0.5 = 0.5 = 50%. Maximum possible efficiency for given temperatures. Memory aid: 'η_Carnot = 1 - T_cold/T_hot; always < 100%'. Thermodynamics calculation frequently tested in competitive exams.