Question

A long spring is attached to a wall at one end. A pulse is sent down the spring. When the pulse reaches the wall it bounces back upside down. At the moment it reaches the wall, a second pulse is sent down the spring. What happens when the two pulse meet? A) The pulses will reflect off each other. B) The pulses generate destructive interference. C) The pulses generate constructive interference. D) The pulses cancel each other out and do not move.

Answer 1

It is given that at the moment the first pulse reaches the wall, a second pulse is sent down the spring. Now, when the two pulses meet they will be subject to the principle of superposition and as one is upside down (the reflected pulse) and the other is up (the second pulse), there will be a nullifying effect and the spring will appear straight for that split moment. Thus we can say that there will be a destructive interference where one pulse will destroy the other or in other words nullify the other's existence. After that moment the pulses will move towards their respective ends as if nothing happened.

Hence, Option B is the correct option.