In Young's experiment the wavelenght of red light is `7.8xx10^(-5) cm ` and that of blue light is `5.2xx10^(-5)` cm. The value of n for which `(n+1)^(th)` blue bright band coincides with `n^(th)` red band is

Options

A. 4
B. 3
C. 2
D. 1

Answer

C

Explanation

`x_((n+1))` for blue `=x_(n)` for red
`(D)/(d)(n+1) lambda_(g)=(D)/(d) n lambda_( r)`
`n lambda_(g)+ lambda_(g)= nlambda_(r)`
`:. N=(lambda_(g))/(lambda-(r)-lambda_(g))=(5.2xx10^(-5))/(7.8xx10^(-5)-5.2xx10^(-5))=2`