Answer to Question #173216 in Optics for Kshitij

Question

An incident wave travelling along a string meets the discontinuity with infinite impedance. Incident wave will be totally reflected back with a change of phase π. True or false

Answer 1

Answer

According to concepts of wave optics

When wave pulse on a string moving from left to right towards the end which is rigidly clamped. When the wave pulse approaches the fixed end, the internal restoring forces which allow the wave to propagate exert an upward force on the end of the string.

Now since the end is clamped, it cannot move.

Now According to Newton's third law, the wall must be exerting an equal downward force on the end of the string.

Therefore we can say This new force creates a wave pulse that propagates from right to left, with the same speed and amplitude as the incident wave, but with opposite polarity.so we can say at a fixed (hard) boundary, the displacement remains zero and the reflected wave changes its polarity (undergoes a 180^o phase change)

sothis is true.