Question

A sine wave is travelling in a medium. The minimum distance between the two particles, always having same speed, is
(a) $\lambda /4$
(b) $\lambda /3$
(c) $\lambda /2$
(d) $\lambda$.

Answer 1

(c) $\lambda /2$

A sine wave has a maxima and a minima and the particle displacement has phase difference of π radians. The speeds at the maximum point and at the minimum point are same although the direction of motion are different. The difference between the positions of maxima and minima is equal to $\lambda /2$.