Question

Two identical light waves, propagating in the same direction, have a phase difference $\delta$. After they superpose the intensity of the resulting wave will be proportional to

• A. $cos\, \delta$
• B. $cos\, (\delta /2)$
• C. $cos^{2} (\delta/2)$
• D. $cos^{2}\delta$

Answer 1

Answer: (C)

$cos^{2} (\delta/2)$

Answer 2

The resulting intensity of two identical light waves, which have a phase difference of δ and propagate in the same direction, is
$I_r=I+I+2I\cosδ=4I\cos^2(\frac{δ}{2})$
Therefore, the resulting intensity of the wave is directly proportional to $\cos^2\frac{δ}{2}$
So, the correct option is (C) : $\cos^2(\frac{δ}{2})$