Q 12-10-115JEE MainJEE Main 2021 (26 Aug, Shift 1)Easy
White light is passed through a double slit and interference is observed on a screen $1.5$ m away. The separation between the slits is $0.3$ mm. The first violet and red fringes are formed $2.0$ mm and $3.5$ mm away from the central white fringes. The difference in wavelengths of red and violet light is (in nm).
Numerical value type. Enter your answer.
Answer: 300
First bright fringe: $y = \dfrac{\lambda D}{d} \Rightarrow \lambda = \dfrac{yd}{D}$.
$$\lambda_r - \lambda_v = \frac{(3.5 - 2.0)\times10^{-3}\times0.3\times10^{-3}}{1.5} = 3\times10^{-7}\ \text{m} = 300\ \text{nm}$$
Solution by Sreeraj P, M.Sc Physics