Question

Two coherent light sources P and Q each of wavelength l are separated by a distance 3l as shown. The maximum number of minima formed on line AB which runs from _  to +  is–

• A. 2
• B. 4
• C. 6
• D. 8

Answer 1

Answer: (C)

6

Answer 2

There can be three minima from central point to 

corresponding to $\frac{\lambda}{2},\frac{3\lambda}{2},\frac{5\lambda}{2}$ path differences.

\ Total number of minima = 2n_max = 6