A convex lens of focal length 20 cm is used as a magnifying glass. For maximum magnification, object should be placed at MCQ with Answer and Explanation

Explanation:
Beat frequency is the absolute difference between two frequencies. Given 4 beats with 256 Hz, the unknown fork is either 256+4=260 Hz or 256-4=252 Hz. Adding wax increases mass, which strictly lowers the frequency of a fork. If it was 252 Hz, lowering it would increase the gap from 256, increasing beats. If it was 260 Hz, lowering it brings it closer to 256, decreasing beats to 2. Thus, it was originally 260 Hz.

Explanation:
R ∝ L/A ∝ 1/d². So R₁/R₂ = (d₂/d₁)² = (1/2)² = 1/4 = 1:4.

Explanation:
Sublimation: solid → gas. Example: dry ice (CO₂), camphor. Deposition is reverse (gas → solid). Melting solid → liquid, evaporation liquid → gas.