Two beams of light having intensities I and 4I interferer to produce a fringe pattern on a screen.The phase difference between the beam is `pi/2` at point Aand `2pi` at point B. Then find out the difference between the resultant intensities at A and B.

Explanation

Resultant intensity `I=I_1I_2+2sqrtI_1sqrtI_2cosphi`
Resultant intensity at point A is `I_A=I+4I+2sqrtIsqrt(4I)cospi/2=5I`
Resultant intensity at point B,
`I_B=I+4I+2sqrtIsqrt(4I)cos2pi=9I`
`(becausecos2pi=1)thereforeI_B-I_A=91-51implies41`