A wave is travelling along a string. At an instant shape of the string is as shown in the enclosed figure. At this instant, point A is moving upwards. Which of the following statements are correct?

Options

A. The wave is travelling to the right
B. displacement amplitude of the wave is equal to the displacement of `B` at this instant
C. At this instant velocity of `C` is also directed upwards
D. phase difference between `A` and `C` may be equal to `pi//2`

Explanation

A is moving upwards, after an elemental time interval , the wave will be as shown dotted in fig. it means, the wave is travelling leftwards. Therefore, option (a) is wrong.
Displacement amplitude of the wave means maximum possible displacement of medium particle, due to propafation of the wave whih is equal to the displacement at B at the instant shown in the figure. hence, opttion (b) is crrect.
From the figure, it is clear that C os ,pving downwards at this instant. hence, option (c ) is wrong.
The phase difference between two points will be equal to `pi//2`if distance between them is equal toi `lambda//4`. between A and C, the distance is less than `lambda//2`. it may be equal to `lambda//4` Hence, phase difference between these two points may be equal to `pi//2`. therefore, option (d) is-correct.