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. `2I`
B. `4I`
C. `5I`
D. `7I`

Answer

B

Explanation

`I(phi)= I_(1)+I_(2) + 2sqrt(I_(1)I_(2)) cos phi` …..(1)
Here, `I_(1) = I and I_(2) = 4I` At point `A, phi = (pi)/(2)`
`I_(A) = I +4I = 5I` , At point `B, phi = pi`
`I_(B) = 1+4I - 4I = I` , `I_(A) - I_(B)` , `=4I`