Two sources of light of intensities I and 4I emit light waves which interfere at a point. Intensity will be ..... At points where the phase difference, is

Options

A. zero `pi`
B. `5 I, (pi)/(2)`
C. `I,(pi)/(2)`
D. `3I,(pi)/(2)`

Answer

B

Explanation

`I=I_(1)=I_(2)+sqrt(I_(1)I_(2)) 2 cos (alpha_(1)-alpha_(2))`
`=I+4I+ sqrt(Ixx4I) 2 "cos"(pi)/(2)`
`=5I`
Thus, intensity will be 5I at points where phases difference is `pi//2`