Question

A charged particle goes undeflected in a region containing electric and magnetic fields. It is possible that-

(i) $\overrightarrow{E}\parallel \overrightarrow{B}$ and $\overrightarrow{v}\parallel \overrightarrow{E}$

(ii) $\overrightarrow{E}\perp \overrightarrow{B}$ and both $\overrightarrow{E}$ and $\overrightarrow{B}\perp \overrightarrow{v}$

(iii) $\overrightarrow{v}\parallel \overrightarrow{B}$ but $\overrightarrow{v}$ is not parallel to $\overrightarrow{E}$

[All the symbols represents their usual meaning]

• A. Only (i) and (ii) are true
• B. Only (ii) and (iii) are true
• C. Only (iii) and (ii) are true
• D. (i), (ii) and (iii) are true

Answer 1

The correct option is A Only (i) and (ii) are true

(i) $\overrightarrow{E}\parallel \overrightarrow{B}$ and $\overrightarrow{v}\parallel \overrightarrow{E}\Rightarrow \overrightarrow{v}\parallel \overrightarrow{E}$ and $\overrightarrow{B}$

$F_{magnetic}=0;F_{electric}=Eq$

Hence, the charge particle moves in an undeflected manner.

(ii)When both $\overrightarrow{E}$ and $\overrightarrow{B}\perp \overrightarrow{v}$

Net force on the particle will be zero i.e., $F_{electric}=F_{magnetic}$

Hence, the charge particle moves in an undeflected manner.

(iii) When $\overrightarrow{v}\parallel \overrightarrow{B}$ but $\overrightarrow{E}$ is not $\parallel \overrightarrow{v}$

$\Rightarrow F_{magnetic}=0$ but $F_{electric}=Eq$

Hence, charge particle drifted along the $\overrightarrow{E}.$

Hence, $\left(A\right)$ is the correct answer.