Two sources are called coherent if they produce waves

Options

A. having a constant phase difference
B. of equal wavelength
C. of equal speed
D. having same shape of wavefront

Answer

A

Explanation

The phase difference `=(2pi)/(lambda)xx`(path difference)
The phase difference in independent of time and depends only on the path difference `(x_(2)-x_(1))`. This hold only if the two sources are coherent i.e. they have a constant fixed phase difference between them.