Q 12-08-169JEE MainJEE Main 2021 (26 Aug, Shift 2)Medium
A light beam is described by $E = 800\sin\omega\left(t - \frac{x}{c}\right)$. An electron is allowed to move normal to the propagation of light beam with a speed of $3\times10^7$ m s$^{-1}$. What is the maximum magnetic force exerted on the electron?
Answer: (B) $12.8\times10^{-18}$ N
$B_0 = \dfrac{E_0}{c} = \dfrac{800}{3\times10^8} = 2.67\times10^{-6}$ T.
$$F_{max} = evB_0 = 1.6\times10^{-19}\times3\times10^7\times2.67\times10^{-6} = 1.28\times10^{-17}\ \text{N} = 12.8\times10^{-18}\ \text{N}$$
Solution by Sreeraj P, M.Sc Physics