A tuning fork produces 4 beats per second when sounded with a 256 Hz standard fork. When a little wax is attached to the tuning fork, the beat frequency drops to 2 beats per second. The original frequency of the tuning fork was: MCQ with Answer and Explanation

Explanation:
Work (W) = F × d × cos(θ). In scenario A, displacement (d) is zero. In scenario B, the applied force (upward) is perpendicular to the displacement (horizontal), so cos(90°) = 0. In scenario C, the centripetal force (gravity) is perpendicular to the satellite's instantaneous direction of motion, so work done is zero. All cases yield zero work.

Explanation:
Using Gauss's law, for an infinite sheet, electric field E = σ/(2ε₀), directed perpendicular to the sheet. This is uniform and independent of distance from the sheet. Option A is for field near conductor surface; C and D are incorrect. Memory aid: 'Infinite sheet: E = σ/(2ε₀); conductor surface: E = σ/ε₀'. This conceptual question tests electrostatics fundamentals, crucial for competitive exams. Always distinguish between conducting and non-conacting sheets, as field expressions differ due to charge distribution.

Explanation:
R ∝ L² (volume constant). L'=3L => R' = 3² × 6 = 9×6 = 54 Ω. Generally, R' = n² R for stretching n times. Important concept.