Two light beams of intersities I and 4I, respectively form interference fringes on a screen. For the two beams phase difference at point a is `(pi)/(2)` and at point B is `pi` . Find the difference in resultant intensities at A and B.

Explanation

Resulatnat intensity at A
`I_(A)=I+4I+2sqrt(I.4I)cos"(pi)/(2)=5I`
Resultant intensity at B
`I_(B)=I+4I+2sqrt(I.4I)cospi=I`
Hence difference in resultant intensities =5I - I=4I.