Q. A beam of light consisting of two wavelengths $650\ nm$ and $520\ nm$ is used to illuminate the slit of a Young’s double slit experiment. Then the order of the bright fringe 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
Explanation
(d) $n\beta_{1} = (n + 1)\beta_{2}$
$\Rightarrow \frac{n \times 650 \times 10^{- 19}D}{d} = \frac{(n + 1) \times 520 \times 10^{- 19} \times D}{d}$
$\Rightarrow n = 4$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.