Q 12-10-031JEE MainJEE Main 2026 (6 Apr, Shift 2)Medium
In a Young double slit experiment, the wavelength of incident light is $6000$ Å, the separation between slits $S_1$ and $S_2$ is $5$ cm and the distance between slits plane and screen is $50$ cm, as shown in the figure below. If the resultant intensity at $P$ is equal to the intensity due to individual slits, the path difference between interfering waves is ______ Å.
Answer: (C) $2000$
Concept. For equal slits $I = 4I_0\cos^2\dfrac{\phi}{2}$; path difference $= \dfrac{\phi}{2\pi}\lambda$.
Step 1. Phase. $I = I_0 \Rightarrow \cos\dfrac{\phi}{2} = \dfrac12 \Rightarrow \phi = \dfrac{2\pi}{3}$.
Step 2. Path difference. $\dfrac{\lambda}{3} = 2000$ Å.
Answer. $2000$ (Option C).
Solution by Sreeraj P, M.Sc Physics
