Question
In a Young's double slit experiment, the intensities at two points, for the path difference $\frac{\lambda}{4}$ and $\frac{\lambda}{3}$ ( $\lambda$ being the wavelength of light used) are $I_1$ and $I_2$ respectively. If $I_0$ denotes the intensity produced by each one of the individual slits, then $\frac{ I _1+ I _2}{ I _0}=..............$

Answer

c
$I =4 I _0 \cos ^2\left(\frac{\Delta \phi}{2}\right)$

$I _1=4 I _0 \cos ^2\left(\frac{\pi}{4}\right)=2 I _0$

$I _2=4 I _0 \cos ^2\left(\frac{2 \pi}{3}\right)= I _0$

$\Rightarrow \frac{ I _1+ I _2}{ I _0}=3$

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