Q. Young's double slit interference experiment is performed using light consisting of $480$ nm and $600$ nm wavelengths to form interference patterns. The least number of the bright fringes of $480$ nm light that are required for the first coincidence with the bright fringes formed by $600$ nm light is
A) $5$
B) $4$
C) $6$
D) $8$
Explanation
[Solution by Dr. Abubacker] Coincidence needs $n_1\lambda_1=n_2\lambda_2$: $480n_1=600n_2\Rightarrow\frac{n_1}{n_2}=\frac54$. The least value is $n_1=5$. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.