A wave is travelling along a string. At an instant, shape of the string is as shown in figure. At this…

A wave is travelling along a string. At an instant, shape of the string is as shown in figure. At this instant, point A is moving upwards. Which of the following statement is correct? Schematic sinusoidal shape of a string: horizontal axis labeled X with origin O at left, vertical axis labeled Y. Points on the curve from left to right labeled A (left rising point), B (crest), C (right descending point). The point O on the axis is shown below A; labels correspond to the printed figure.
  1. (a) The wave is travelling to the right
  2. (b) Displacement amplitude of the wave is equal to displacement of B at this instant
  3. (c) At this instant, velocity of C is also directed upwards
  4. (d) Phase difference between A and C may be equal to π/2

Solution

From the figure (A moving upward) the instantaneous shape after a short time shows the wave peak shifted left — the wave is travelling left. Thus option (a) (which presumably asserted rightward travel) is wrong. The displacement amplitude is the maximum displacement of medium particles and equals the instantaneous displacement at point B in the figure, so statement about displacement amplitude (b) is correct. At the instant shown point C is moving downward, so any statement claiming upward motion of C is wrong. Hence the correct choice is the one indicated.

Practice more Waves and Sound questions on Aicharya