A wave equation is represented as
`r = A sin [ alpha (( x - y)/(2)) ] cos [ omega t - alpha (( x + y)/(2))]`
where ` x` and `y` are in metres and t in seconds . Then ,

Options

A. the wave is a stationary wave.
B. the wave is a progressive wave propagating along ` + x - axis`.
C. the wave is a progressive wave propagating at right angle to the ` + x - axis`
D. all points lying on line ` y = x + ( 4 pi //alpha)` are always at rest.

Answer

D

Explanation

For `y = x + ( 4 pi)/(alpha)`
`(delta r)/(delta t) = 0`
i.e., all points lying on the ` y = x + ( 4pi)/(alpha)` are always at rest.