The phenomenon by which heat is transferred through empty space without the need for a material medium is known as: MCQ with Answer and Explanation

Explanation:
h = ½gt² => t = √(2h/g) = √(40/10) = √4 = 2 s. Free fall formula. Final velocity v = gt = 20 m/s.

Explanation:
J. J. Thomson measured the specific charge (e/m) of electrons in 1897 using cathode ray tube experiments with electric and magnetic fields. Millikan later measured the charge e (oil drop experiment), allowing mass calculation. Rutherford discovered nucleus; Bohr developed atomic model. Memory aid: 'Thomson = e/m; Millikan = e'. This history-based question tests knowledge of experimental physics milestones, frequently appearing in competitive exams. Always link scientists to their specific measurements: Thomson (e/m), Millikan (e), Chadwick (neutron).

Explanation:
For spring-mass system undergoing SHM, time period T = 2π√(M/k), derived from F = -kx = Ma ⇒ a = -(k/M)x, so ω² = k/M, T=2π/ω=2π√(M/k). Option B has inverse ratio; C misses factor 2; D is for pendulum. Memory tip: 'Spring: T ∝ √(M/k); Pendulum: T ∝ √(l/g)'. This standard formula is frequently tested in oscillations sections of competitive exams. Always verify dimensions: √(kg / (N/m)) = √(kg·m/N) = √(s²) = s, correct for time period.