Question

A charged particle is released from rest in a region of steady and uniform electric and magnetic fields which are parallel to each other. The particle will move in a

• A. helix
• B. cycloid
• C. straight line
• D. circle

Answer 1

Answer: (C)

$\overrightarrow{E}\parallel \overrightarrow{B}$
$F_E=q\overrightarrow{E}$
$F_B= q(\vec{v} \times \vec{B}$
given $\overrightarrow{v}$ is parallel to $\overrightarrow{B}$
$\Rightarrow F_B=0$ since $\sin \theta =\sin 0^{\circ }=0$
$\therefore$ the charged particle will accelerate and move in a straight line.