Magnetic Effects & Magnetism

JEE Main level, single correct, medium

128 of 276

Question 128 of 276

An electron is moving along the positive x-axis. If 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 x-axis
E.The electron will move along circular path in magnetic field
Choose the correct answer from the option given below:

Show answer and solution

Answer: (C) B and E only

The Lorentz force is given by
F⃗=qv⃗×B⃗\vec{F}=q\vec{v}\times \vec{B}
=−ev⃗×B⃗=-e\vec{v}\times \vec{B}
So, F^=i^×k^=−j^\hat{F}=\hat{i}\times \hat{k}=-\hat{j}.
F⃗isalong−yaxis\vec{F}is\text{along}-y\text{axis}
As the magnetic field is perpendicular to the velocity, motion would be circular.

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