Q. Two slits are separated by a distance of $0.5\ mm$ and illuminated with light of $\lambda = 6000\ \mathring{\mathrm{A}}$. If the screen is placed $2.5\ m$ from the slits. The distance of the third bright fringe from the centre will be
A) $1.5\ mm$
B) $3\ mm$
C) $6\ mm$
D) $9\ mm$
Explanation
(d) Distance of the $n^{th}$ bright fringe from the centre $x_{n} = \frac{n\lambda D}{d}$
$\Rightarrow x_{3} = \frac{3 \times 6000 \times 10^{- 10} \times 2.5}{0.5 \times 10^{- 3}} = 9 \times 10^{- 3}m = 9mm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.