# In a double slit experiment , when light of wavelength 400 nm was used , the angular width of the first minima formed on a screen palced 1 m away , was found to be $0.2 \degree$ . what will be the angular  width of the first minima , if the entire experimental apparatus is immersed in water ?  $0.15 \degree$ $0.05 \degree$ $0.1 \degree$

Refractive index -

$\mu = \frac{c}{v}$

- wherein

$c=$ speed of light in vacuum.

$v=$ speed of light in medium.

Young Double Slit Experiment -

- wherein

$y=\Delta x\cdot \left ( \frac{D}{d} \right )$

$y=$ Distance of a point on screen from central maxima

$\Delta x=$ Path difference at that point

Fringe Width in a medium -

${\beta }'= \frac{\beta }{\mu }$

- wherein

Since wavelength in a medium become $\lambda = \frac{\lambda _{o}}{\mu }$

Angular width =$\theta \ \alpha \ \ \lambda$

and $\mu =\frac{c}{v}=\frac{\lambda _1}{\lambda _2}=\frac{\theta _1}{\theta _2}$

$\theta _2=\frac{\theta _1 }{\mu }\Rightarrow \frac{0.2*3}{4}=0.15^0$

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