Power P = 1/f (in meters). P = -2 D ⇒ f = 1/(-2) = -0.5 m = -50 cm. Negative focal length indicates diverging (concave) lens. Convex lenses have positive power. Option A correctly states concave lens with |f| = 50 cm. Memory tip: 'Negative power = concave lens; f(in cm) = 100/P(in D)'. This direct application of lens power definition is common in competitive exams. Always convert diopters to focal length carefully, noting sign convention: negative for diverging lenses, positive for converging.
Explanation:
Newton's Law of Cooling is a practical approximation stating that the rate of heat loss of a body is directly proportional to the difference in temperatures between the body and its immediate environment, provided this temperature difference is relatively small. The equation is dQ/dt = -k(T_body - T_surroundings).
Explanation:
Equipotential: ΔV = 0 ⇒ W = qΔV = 0. Electric field perpendicular to equipotentials. Memory aid: 'Equipotential: no work to move charge along it'. Electrostatics concept frequently tested in competitive exams.
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