In a Young's double slit experiment, when light of wavelength 400 nm was used, the angular width of the first minima formed on a screen placed 1 m away, was found to be 0.2⁰. What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water? (Take, for water $\mu$ = 4 13) [NEET 2019]

The angular width in YDSE is given by

$\theta =\frac{\beta }{D}$

where, $\beta$ is the separation between two fringes and D is the distance between the slits and screen. If YDSE apparatus is immersed in a liquid of refractive index $\mu$ then the wavelength of light and hence the angular width decreases $\mu$ times.

i.e.,   $\theta \text{'}=\frac{\beta }{\mu D}=\frac{\theta }{\mu }$

Here,  $\mu$ (for water) = 4/3 and $\theta$ = 0.2⁰

$\Rightarrow \theta \text{'}=\frac{0.2°}{4/3}=0.15°$

$\Rightarrow \theta \text{'}=\frac{0.2°}{4/3}=0.15°$