Q. In Young’s experiment, the distance between slits is $0.28\ mm$ and distance between slits and screen is $1.4\ m$. Distance between central bright fringe and third bright fringe is $0.9\ cm$. What is the wavelength of used light
A) $5000\ \mathring{\mathrm{A}}$
B) $6000\ \mathring{\mathrm{A}}$
C) $7000\ \mathring{\mathrm{A}}$
D) $9000\ \mathring{\mathrm{A}}$
Explanation
(b) Position of $3^{rd}$ bright fringe $x_{3} = \frac{3D\lambda}{d}$
$\Rightarrow \lambda = \frac{x_{3}d}{3D} = \frac{(0.9 \times 10^{- 2}) \times (0.28 \times 10^{- 3})}{3 \times 1.4} = 6000\mathring{\mathrm{A}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.