Two beam of light having intensities I and 4I interfere to produce a fringe pattern on a screen. The phase difference between the beams is `(pi)/(2)` at point A and `pi` at point B. Then the difference between resultant intensities at A and B is : `(2001 , 2M)`

Options

A. (a) `2I`
B. (b) `4I`
C. (c) `5I`
D. (d) `7I`

Answer

B

Explanation

At point A, resultant intensity
`I_A=I_1+I_2=5I`, and at point B
`I_B=I_1+I_2+2sqrt(I_1I_2)cos pi=5I+4I`
`I_B=9I` so `I_B-I_A=4I`.