Discussion Forum



1)

Two identical light waves having phase difference '$\phi$' propagate in same direction, when they superpose , the intensity of resultant wave is proportional to 


A) $\cos^{2}\phi$

B) $\cos^{2}\frac{\phi}{2}$

C) $\cos^{2}\frac{\phi}{3}$

D) $\cos^{2}\frac{\phi}{4}$

Answer:

Option B

Explanation:

For two  coherent sources , the resultant intensity is given as,

$l_{R}=l_{1}+l_{2}+2\sqrt{l_{1}l_{2}}\cos \phi$

 $\therefore$      Fror two identical light waves,

$l_{1}=l_{2}=l$

$\Rightarrow$    $l_{R}=4l\cos^{2}\frac{\phi}{2}$

$\therefore$    $l_{R}\propto\cos^{2}\frac{\phi}{2}$