In a biprism expeirment to determine the wavelenght of light, the distance between slit and eyepiece is 1,. Wavelenght of light used is 5600Å. When a convex lens is kept at a distance of 30 cm from the slit, the distance of fourth the two images is 0.7 mm. The distance of fourth dark band from the central bright band is

Options

A. 6.5 mm
B. `4.5 mm`
C. `7.5 mm`
D. `7.0 mm`

Answer

A

Explanation

`(d_(1))/(d)=(v)/(u):.d=(0.7xx30)/(70)=0.3mm`
`x_(4d)=3.5beta=3.5(Dlamda)/(d)=(3.5xx1xx5.6xx10^(-7))/(3xx10^(4))`
=6.5mm