Q14.19: NCERT Physics - Part 2 WAVES 14.19 Solution: Explain why (or how): (a) in a sound wave, a displacement node…

**Answer:** (a) Pressure and displacement are out of phase. (b) Echolocation. (c) Different overtones. (d) Gases lack shear elasticity. (e) Different wavelengths travel at different speeds. **Step-by-Step Explanation:** (a) At a displacement node, particles do not move, so the pressure variation is maximum (antinode). At a displacement antinode, particles move freely, so pressure variation is minimum (node) [citation:4]. (b) Bats emit ultrasonic waves and detect the reflected waves. The time delay gives distance, and the nature of the echo gives information about the obstacle [citation:4]. (c) The quality of sound depends on the number and relative strengths of overtones. Sitar and violin produce different overtones even for the same fundamental frequency [citation:4]. (d) Solids have both volume and shear elasticity, so they support longitudinal and transverse waves. Gases have only volume elasticity, so only longitudinal waves propagate [citation:4]. (e) In a dispersive medium, waves of different wavelengths travel at different speeds. A pulse, which is a superposition of many wavelengths, gets distorted as it propagates [citation:4].