Q 12-11-039JEE MainJEE Main 2026 (5 Apr, Shift 2)Easy
An electron is travelling with a velocity $v$ in free space and when it enters a medium, its velocity is reduced by $20\%$. The de Broglie wavelength of electron in the medium is $\alpha\lambda_0$, where $\lambda_0$ is its de Broglie wavelength in free space. The value of $\alpha$ is ______.
Answer: (C) $1.25$
$\lambda = \dfrac{h}{mv} \propto \dfrac{1}{v}$. With $v' = 0.8v$: $\lambda = \dfrac{\lambda_0}{0.8} = 1.25\lambda_0$.
Solution by Sreeraj P, M.Sc Physics