Question

Bi-prism is kept 10 cm away from the slit illuminated by monochromatic light of wavelength 5896Å. the width of the fringes obtained on screen placed at a distance of 90 cm from the biprism is( 9*10^-4)m. What is the distance between two coherent sources.

Answer 1

As per the question,

distance $(a_1)= 10cm$

wavelength $(\lambda)=5896Å.$

The width of the fringe obtained at the distance $(a_2)=90cm$

width of the fringe $(\beta)=9\times10^{-4}m$

distance between two co-herent source =?

$D=a_1+a_2= 10cm+90cm =100cm$

$\Rightarrow (\beta)=\frac{\lambda D}{2d}$

$\Rightarrow 2d=\frac{\lambda D}{\beta}$

$\Rightarrow 2d =\frac{5896\times 10^{-10}\times 100 \times 10^{-2}}{9\times 10^{-4}}m$

$=0.655 mm$