When a source of sound moves towards a stationary observer, the apparent frequency: MCQ with Answer and Explanation

Explanation:
Potentiometer measures EMF and internal resistance. Formula: r = R(L₁ - L₂)/L₂, where R is shunt resistance, L₁ initial balancing length, L₂ after shunting. Here R=2Ω, L₁=60 cm, L₂=40 cm. Thus r = 2×(60-40)/40 = 2×20/40 = 1Ω. This derives from terminal voltage V = E - Ir and potentiometer principle V ∝ balancing length. Memory tip: 'r = R(L₁/L₂ - 1)'. This advanced numerical tests potentiometer applications, common in competitive exams for experimental physics. Always verify the formula derivation to avoid misapplication.

Explanation:
Polarization (restriction of electric field oscillation to one plane) is possible only for transverse waves, where oscillations are perpendicular to propagation direction. Longitudinal waves (e.g., sound) cannot be polarized as oscillations are along propagation. This was key evidence for light's transverse wave nature. Memory aid: 'Polarization ⇒ transverse wave; light is EM transverse wave'. This conceptual question tests wave optics fundamentals, frequently examined in competitive exams. Always distinguish wave types: transverse (light, string waves) vs longitudinal (sound, spring waves).

Explanation:
Radiation transfers heat via electromagnetic waves and requires no medium, thus works in vacuum (e.g., solar energy reaching Earth). Conduction needs direct contact between particles; convection requires fluid movement. Vacuum lacks matter for conduction/convection. Memory tip: 'Radiation = only mode in vacuum'. This fundamental distinction is frequently tested in competitive exams. Applications include thermos flasks (minimizing all three modes) and space technology. Always recall that radiation speed is light speed, while conduction/convection are much slower.