Correct Answer - b
`y_(1)=a_(1)sin(omegat-(2pix)/(lambda))`
`y_(2)=a_(2) sin(omegat-(2pix)/(lambda)+phi+(pi)/(2))`
phase difference
`=(omegat-(2pix)/(lambda)+phi+(pi)/(2))-(omegat-(2pix)/(lambda))=(phi+(pi)/(2))`
path difference `=(lambda)/(2pi)xx`phase differance` =(lambda)/(2pi)(phi+(pi)/(2))`