Q. An electron is travelling along the $x$-direction. It encounters a magnetic field in the $y$-direction. Its subsequent motion will be
A) Straight line along the $x$-direction
B) A circle in the $xz$-plane
C) A circle in the $yz$-plane
D) A circle in the $xy$-plane
Explanation
(b) $\overrightarrow{F} = - e\left( \overrightarrow{v} \times \overrightarrow{B} \right) \Rightarrow \overrightarrow{F} = - e\left\lbrack v\widehat{i} \times B\widehat{j} \right\rbrack = evB\lbrack - \widehat{k}\rbrack$
$i.e.$ Force on electron is acting towards negative $z$-axis. Hence particle will move in a circle in $xz$-plane
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.