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. 9I
B. 5I
C. 3I
D. I

Answer

B

Explanation

`I_(1) = I, I_(2) = 4I, phi = (pi)/(2)`
The resultant intensity `I_(R)` is given by
`I_(R) = I_(1) + I_(2) + 2 sqrt(I_(1) I_(2)) cos phi`
`= I + 4I + 2sqrt(I xx 4I) xx cos 90^(@)`
`:. I_(R) = 5I " " ( :' cos 90^(@) = 0)`