The half-life of a radioactive substance is 5 years. The fraction disintegrated after 15 years is MCQ with Answer and Explanation

Explanation:
Speed constant implies magnitude of velocity constant, so kinetic energy (½mv²) is constant. Velocity changes due to direction change. Acceleration (centripetal) is directed towards centre, changes direction. Linear momentum vector changes. So only kinetic energy remains constant.

Explanation:
λ = h/(mv) = 6.63×10⁻³⁴/(1×10) = 6.63×10⁻³⁵ m. Extremely small, not observable. For electron it's significant. de Broglie hypothesis: matter waves. This is modern physics.

Explanation:
Myopia (nearsightedness): far point reduced; corrected by concave (diverging) lens to shift image to retina. Hypermetropia uses convex lens. Memory tip: 'Myopia = near-sighted ⇒ concave lens; Hyper = far-sighted ⇒ convex'. Vision defect correction frequently tested in competitive exams to assess application knowledge.