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) $1.25$
Concept. $\lambda=\dfrac{h}{mv}\propto\dfrac1v$.
Step 1. New speed. $0.8v$, so $\lambda=\dfrac{\lambda_0}{0.8}=1.25\lambda_0$.
Answer. Option C.
Solution by Sreeraj P, M.Sc Physics
