A block of mass 'm' is placed on a rough inclined plane of inclination theta. If the block is just on the verge of sliding down, the coefficient of static friction (mu) is equal to: MCQ with Answer and Explanation

Explanation:
For spherical mirrors (concave or convex), focal length f = R/2, where R is radius of curvature. This holds under paraxial approximation (small angles). Derivation uses geometry of reflection and small-angle approximations. Memory tip: 'Mirror: f = R/2; Lens: 1/f = (n-1)(1/R₁ - 1/R₂)'. This fundamental relation is frequently tested in optics sections of competitive exams. Always note sign conventions: f negative for convex mirrors, positive for concave; R follows same sign as f.

Explanation:
In any collision (elastic or inelastic), the total linear momentum is always conserved, provided no external forces act on the system. However, a perfectly elastic collision is specifically defined as one in which there is absolutely no loss of kinetic energy. Therefore, both total linear momentum and total kinetic energy are conserved.

Explanation:
Sir C.V. Raman discovered inelastic scattering of light (Raman effect) in 1928, received Nobel in 1930. Used to study molecular structure. Photoelectric effect: Einstein. Electron: J.J. Thomson. Fission: Hahn and Strassmann.