Two coherent light beams of intensities I and 4I superpose in a region. Find the maximum and minimum possible intensities due to superposition in this region.

Options

A. 5I , - 3I
B. 9I , I
C. 9I, -I
D. 5I, 3I

Answer

B

Explanation

During interference intensity theorem
`I_(0) = I_(1) + I_(2) + 2 sqrt(I_(2)I_(1)) cos alpha`
Clearly, `I_(0)` is mximum when `cos alpha = 1` and minimum when `cos alpha = 1`
`I_("max") = 4I + I + 2sqrt(4I xx I) = 9I`
`I_("min") = 4I + I - 2 sqrt(4I xx I) = I`