Question

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

Answer 1

Correct Answer - B
Here, `I_(1)=I,I_(2)=4I, phi_(1)=(pi)/(2),phi_(2)=pi`
`I_(A)=I_(1)+I_(2)+2sqrt(I_(1)I_(2))cosphi_(1)`
` " " =I+4I+2sqrt(Ixx4I)"cos"(pi)/(2)=5I`
`I_(B)=I_(1)+I_(2)+2sqrt(I_(1)I_(2))cosphi_(2)`
` " " =I+4I+2sqrt(Ixx4I)"cos"pi=5I-4I=I`
` :. I_(A)-I_(B)=5I - I = 4I`