Q 12-10-029JEE MainJEE Main 2026 (6 Apr, Shift 1)Easy
In interference experiment the path difference between two interfering waves at a point $A$ on the screen is $\lambda/3$, where $\lambda$ is the wavelength of these waves, and at another point $B$ the path difference is $\lambda/6$. The ratio of intensities at points $A$ and $B$ is ______.
Answer: (C) $1/3$
$I = I_{\max}\cos^2\dfrac{\phi}{2}$ with $\phi = \dfrac{2\pi}{\lambda}\Delta x$.
At $A$: $\phi = \dfrac{2\pi}{3}$, $\cos^2 60^\circ = \dfrac{1}{4}$. At $B$: $\phi = \dfrac{\pi}{3}$, $\cos^2 30^\circ = \dfrac{3}{4}$.
$\dfrac{I_A}{I_B} = \dfrac{1/4}{3/4} = \dfrac{1}{3}$.
Solution by Sreeraj P, M.Sc Physics