In Young's experiment, using red light `(lambda=6600overset(@)A),` 60 fringes are seen in the field of view. How many fringes will be seen by using violet light `(lambda=4000overset(@)A)` ?

Options

A. 10
B. 20
C. 45
D. 90

Answer

D

Explanation

Using red light `(lambda=6600 overset(@)(A))` 60 fringes are seen.
Hence, range of field of view is
`" "60 times w=60 times (Dlambda)/d`
using light of wavelength `lambda.`, n fringes are seen, then
`rArr" "60 times (Dlambda)/d=n times (Dlambda.)/d`
`" "60 times lambda=n times lambda.`
`rArr" "n=60 times lambda/(lambda.)=60 times 6600/4400=90`