A convex lens is immersed in water. Its focal length MCQ with Answer and Explanation

Explanation:
This is based on the conservation of angular momentum (L = Iω), where 'I' is the moment of inertia and 'ω' is angular velocity. When the boy extends his arms, mass moves further from the axis of rotation, increasing his moment of inertia (I). Since 'L' is conserved, an increase in 'I' must result in a decrease in angular velocity (ω).

Explanation:
Hygrometer measures atmospheric humidity (water vapor content). Barometer: pressure; Hydrometer: liquid density; Anemometer: wind speed. Memory tip: 'Hygro = moisture; meter = measure'. Instrument identification frequently tested in competitive exams to verify practical physics knowledge.

Explanation:
When light passes from a rarer medium (air) to a denser medium (glass), its speed decreases due to the higher refractive index. Wavelength is directly proportional to speed, so it also decreases. However, the frequency depends only on the source of light and remains absolutely constant during refraction across any boundary.