Q. A charged particle is moving in the presence of electric field $\overrightarrow{\mathbf{E}}$ and magnetic field $\overrightarrow{\mathbf{B}}.$ The directions of $\overrightarrow{\mathbf{E}}\ $and $\overrightarrow{\mathbf{B}}$ are such that the charged particle moves in a straight line and its speed increases. The relations amongst $\overrightarrow{\mathbf{E}}$ ,$\ \overrightarrow{\mathbf{B}}$ and velocity $\overrightarrow{\mathbf{v}}$ must be such that
A) $\overrightarrow{\mathbf{E}}\mathbf{\bullet}\overrightarrow{\mathbf{B}} = 0,\ \overrightarrow{\mathbf{v}}$ is arbitrary
B) $\overrightarrow{\mathbf{E}}\mathbf{\ },\overrightarrow{\mathbf{B}}$ and $\overrightarrow{\mathbf{v}}$ are all parallel to each other
C) $\overrightarrow{\mathbf{E}}\mathbf{\bullet}\overrightarrow{\mathbf{v}} = 0;\overrightarrow{\mathbf{B}}\mathbf{\bullet}\overrightarrow{\mathbf{v}} = 0$ but $\overrightarrow{\mathbf{E}}\mathbf{\bullet}\overrightarrow{\mathbf{B}} \neq 0$
D) $\overrightarrow{\mathbf{v}}$ is parallel to $\overrightarrow{\mathbf{E}}$ and perpendicular to $\overrightarrow{\mathbf{B}}$
Explanation
(b) A charged particle moves along a straight line with acceleration, hence electric field should be parallel to the direction of motion of charged particle and no force should act on charged particle due to magnetic field. It will be so if charged particle is moving parallel to the direction of magnetic field
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.