Question

If intensity of each wave in the observed interference pattern in Young's double slit experiment is $I_0$, then for some point P where the phase difference is $\varphi$, resultant intensity $I$ will be:

• A. $I=I_0\cos \varphi$
• B. $I=I_0{\cos }^2\varphi$
• C. $I=I_0(1+\cos \varphi )$
• D. $I=2I_0(1+\cos \varphi )$

Answer 1

The correct option is D $I=2I_0(1+\cos \varphi )$

Resultant intensity,
$I=I_1+I_2+2\sqrt{I_1{I}_2}\cos \varphi$
$I=I_0+I_0+2\sqrt{I_0{I}_0}\cos \varphi$
$I=2I_0(1+\cos \varphi )$