Question

Light waves from two coherent sources having intensities $I$ and $2I$ cross each other at a point with a phase difference of ${60}^o$. What is the resultant intensity at the point?

Answer 1

Given - $I_1=I,I_2=2I,\theta ={60}^o$

We have , resultant intensity

$I_R=I_1+I_2+2\sqrt{I_1{I}_2}\cos \theta$

or $I_R=I+2I+2\sqrt{I\times 2I}\cos 60$

or $I_R=3I+2I\sqrt{2}\times 1/2=I(3+\sqrt{2})$