Question

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 figure of the longer wavelength that coincide with a bright fringe of the shorter wavelength at the least distance from the central maximum is:-

• A. $1$
• B. $2$
• C. $3$
• D. $4$

Answer 1

Answer: (D)

$4$

$n{\beta }_1=(n+1){\beta }_2$

$\Rightarrow \frac{n\times 650\times {10}^{-19}D}{d}$

$=\frac{(n+1)\times 520\times {10}^{-19}\times D}{d}$

$\Rightarrow n=4$