Q. In a Young’s experiment, two coherent sources are placed 0.90 mm apart and the fringes are observed one meter away. If it produces the second dark fringe at a distance of 1 mm from the central fringe, the wavelength of monochromatic light used will be
A) $60 \times 10^{- 4}\ cm$
B) $10 \times 10^{- 4}\ cm$
C) $60 \times 10^{- 5}\ cm$
D) $6 \times 10^{- 5}\ cm$
Explanation
(d) $x = (2n - 1)\frac{\lambda}{2}\frac{D}{d}\ $
$\lambda = \frac{2xd}{(2n - 1)D} = \frac{2 \times 10^{- 3} \times 0.9 \times 10^{- 3}}{(2 \times 2 - 1) \times 1}$
$6 \times 10^{- 7}\ m = 6 \times 10^{- 5}\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.