Question

Explain in simpler words-
If a transverse wave is reflected from a rarer medium, the crest is reflected as crest and the trough as trough. But when a longitudinal wave is reflected from a rarer medium, the compression is reflected as rarefaction and vice versa.

Answer 1

A wave pulse was generated at the left end which travelled on the string towards right . When the pulse reaches a particular elements , the forces on the element from the left part of the string and from the right part act in such away that the element is disturbed according to the shape of the pulse .
The situation is different when the pulse reaches the right end which is clamped at the wall . The element at the right end exerts a force on the clamp and the clamp exerts equal and opposite force on the element . The element at the right end is thus acted upon by the force from the string left to it and by the force from the clamp . As this end remains fixed , the two forces are opposite to each other . The forces from the left part of the string transmits the forward wave pulse and hence , the force exerted by the clamp sends a return pulse on the string whose shape is similar to to the original pules but is inverted . The original pules tries to pull the element at the fixed end up and the return pulse sent by the clamp tries to pull it down . The resultant displacement is zero . Thus , the wave is reflected from the the fixed end and the reflected wave is inverted with respect to the original wave . When there exists a discontinuity in the medium, the wave gets reflected .