Q 12-04-216JEE MainJEE Main 2019 (11 Jan, Shift 1)Easy
In an experiment, electrons are accelerated, from rest, by applying a voltage of $500$ V. Calculate the radius of the path if a magnetic field $100$ mT is then applied. [Charge of the electron $= 1.6\times10^{-19}$ C, mass of the electron $= 9.1\times10^{-31}$ kg]
Answer: (D) $7.5\times10^{-4}$ m
Momentum after acceleration: $p = \sqrt{2meV}$.
$$r = \frac{p}{eB} = \frac{\sqrt{2\times9.1\times10^{-31}\times1.6\times10^{-19}\times500}}{1.6\times10^{-19}\times0.1}$$
$$= \frac{1.21\times10^{-23}}{1.6\times10^{-20}} \approx 7.5\times10^{-4}\ \text{m}$$
Solution by Sreeraj P, M.Sc Physics