An electron is moving along the positive x -axis. If the uniform… | JEE Main 2023 (13 Apr, Shift 2)

Q42JEE Main 2023 · 13 APR · SHIFT 2Easy

Moving Charge in a Magnetic Field

An electron is moving along the positive $\mathrm{x}$ -axis. If the uniform magnetic field is applied parallel to the negative z-axis, then

A. The electron will experience magnetic force along positive y-axis

B. The electron will experience magnetic force along negative y-axis

C. The electron will not experience any force in magnetic field

D. The electron will continue to move along the positive $\mathrm{x}$ -axis

E. The electron will move along circular path in magnetic field

Choose the correct answer from the options given below:

Show answer and solution

Answer: (c)

$\vec{F} = -e(\vec{v} \times \vec{B})$ with $\vec{v} = v\hat{i}$ , $\vec{B} = -B\hat{k}$ .
$\hat{i} \times (-\hat{k}) = \hat{j}$ , so $\vec{v} \times \vec{B} = vB\hat{j}$ and $\vec{F} = -evB\hat{j}$ : along $-y$ (B true, A false).
Force is perpendicular to velocity, so the electron moves in a circle (E true; C, D false).
So the answer is (c) B and E only.

Moving Charge in a Magnetic Field question from JEE Main 2023 (13 Apr, Shift 2)