When a charged particle moves in an elecltric or a magnetic field, its speed is `v` and acceleration is `a`

Options

A. In a magnetic field, v is constant if the particle moves in a circular path, and variable if it moves in a helical path
B. In a magnetic field, v is always constant, a may or may not be zero
C. In an electric field, v can never remain constant
D. In a uniform electric field, a must be constant in magnitude and direction

Answer

B, C, D

Explanation

In an electric field `, barF=qbarEimpliesmbara=qbarE:.bara=(qbarE)/m`
Since there is acceleration, velocity cannot remain constant and also the acceleration. is constant in magnitude & direction.
In a magnetic field. `barF=q(barvxxbarb)rarrbara=q/m(barvxxbarB)`
So `bara` may not be zero and v is always constant whether the particle is || or `_|_` or at any angle to the field.