Question

A charged particle is at rest, in the region where magnetic field and electric field are parallel. The particle will move in along,

• A. a straight line
• B. a circle
• C. an ellipse
• D. None of these

Answer 1

The correct option is A a straight line

As the charge is at rest initially, so, $F_m=0$ and $F_e=qE$.

The electric field will accelerate the charged particle either along or in the opposite direction of electric field, depending upon whether the charge is positive or negative.

In either cases, $F_m$ will still be equal to zero as
${\overrightarrow{F}}_m=q(\overrightarrow{v}\times \overrightarrow{B})$
Here, $F_m=0$ when $\overrightarrow{v}$ and $\overrightarrow{B}$ are either parallel or anti-parallel.

So the charged particle will move along a straight line.

Hence, $\left(A\right)$ is the correct answer.$$\begin{array}{c}\text{Why this question ?}\\ \text{Use Lorentz force in deciding direction of motion of charged particle}\end{array}$$