Ideal gas internal energy depends on: MCQ with Answer and Explanation

Explanation:
Spherical mirrors: f = R/2 under paraxial approximation. Derived from geometry of reflection. Memory tip: 'Mirror: f = R/2; sign: concave +, convex -'. Optics formula frequently tested in competitive exams.

Explanation:
Work done = F·s = Fs cosθ. Coolie applies vertical force to support weight, displacement horizontal, angle 90°, cos90°=0, work zero. No displacement of force direction. Pushing wall: displacement zero, also zero work. But option A is standard example. Pushing wall also zero, but question expects one answer. I'll adjust: I'll remove 'pushing a wall' to avoid ambiguity. I'll replace with 'A satellite revolving around Earth in circular orbit' etc. However, here I'll keep A, note that pushing wall also has zero displacement, but the question lists specific cases, only one may be correct. Actually, in pushing wall, wall doesn't move, work zero, but often they consider pushing wall as no work. However, option D 'Pushing a wall' might also be zero. To avoid two correct, I'll change D to 'Throwing a ball upward' so only A is zero. I'll modify the question: D: 'Throwing a ball upward' (work positive). So answer A. Let's do that.

Explanation:
J.J. Thomson measured e/m using cathode ray deflection (1897). Millikan later measured e (oil drop). Memory aid: 'Thomson = e/m; Millikan = e'. Experimental physics history frequently tested in competitive exams.