Q 12-10-121JEE MainJEE Main 2020 (9 Jan, Shift 2)Easy
In a Young's double slit experiment $15$ fringes are observed on a small portion of the screen when light of wavelength $500$ nm is used. Ten fringes are observed on the same section of the screen when another light source of wavelength $\lambda$ is used. Then the value of $\lambda$ is (in nm) ______.
Numerical value type. Enter your answer.
Answer: 750
Fringe width $\beta \propto \lambda$. The same length holds $15\beta_1 = 10\beta_2$:
$$\lambda = \frac{15}{10}\times500 = 750\ \text{nm}$$
Solution by Sreeraj P, M.Sc Physics