(a) Two monochromatic waves emanating from two coherent sources have the displacements represented by
`Y_1 = a cosomegat`
and `Y_2 = a cos(omegat+phi)`,
where `(phi)` is the phase difference between the two waves. Show that the resultant intensity at a point due to their superposition is given by `I =4I_0cos^2 phi//2`, where `I_0 = a^2`.
(b) Hence, obtain the conditions for constructive and destructive interference.