Question

A charged particle moves with constant velocity in a region where no effect of gravity is felt but an electrostatic field $\vec{E}$ together with a magnetic field $\vec{B}$ may be present. Then which of the following cases are possible ?

• A. $\vec{E}\ne 0,\vec{B}\ne 0$
• B. $\vec{E}\ne 0,\vec{B}=0$
• C. $\vec{E}=0,\vec{B}=0$
• D. $\vec{E}=0,\vec{B}\ne 0$

Answer 1

Answer: (A), (C), (D)

If a charged particle is moving in a gravity-free space without changing its velocity, then three cases possible
(i) Particle can move with constant velocity in any direction, if $\vec{E}=0,\vec{B}=0$.
(ii) If $\vec{E},\vec{B}$ are having values such that $qE=qvB$ and hence both forces (Force due to magnetic field and force due to electric field) acts in such a way that they cancel each other, in this case also particle can move with uniform velocity.
(iii) If $\vec{E}=0,\vec{B}\ne 0$ and $\vec{B}$ is such that it acts in the direction of velocity then magnetic force would be zero and hence velocity can remain constant.