Question

A charged particle moves in a gravity free space where an electric field of strength E and a magnetic field of induction B exist. Which of the following statement is/are correct?

• A. If $E\ne 0$ and $B\ne 0$, velocity of the particle may remain constant
• B. if $E=0$, the particle cannot trace a circular path
• C. if $E=0$, kinetic energy of the particle remains constant
• D. none of these

Answer 1

Answer: (A), (C)

if $E=0$, kinetic energy of the particle remains constant
If $E\ne 0$ and $B\ne 0$, velocity of the particle may remain constant

a. Velocity of the particle can be constant if the electric force balances the magnetic force, i.e., $q\overrightarrow{E}=q\overrightarrow{v}\times \overrightarrow{B}$.
b. If $E=0$, the particle can trace circular path if $v\perp B$.
c. If $E=0$, kinetic energy remains constant, because magnetic force is not doing any work.