A beam of light consisting of two wavelength `650nm` and `520nm` is used to illuminate the slit of a Young's double slit experiment. Then the order of the bright firnge of the longer wavelength that coincide with a bright fringe of the shorter wavelength at the least distance from the central maximum is

Options

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

Answer

D

Explanation

According to the question, `n beta=(n+1)beta_(2)`
`(n xx lambda_(1)D)/(d)=((n+1)lambda_(2)D)/(d)`
`rArr (nxx650xx10^(-9)xxD)/(d)=((n+1)xx520xx10^(-9))/(d)xxD`
`rArr n =4`