Question

A proton moving with a constant speed passes through a region of space without any change in its speed. If $E$ and $B$ represent the electric and magnetic fields respectively, this region of space may have
a) $B\ne 0,E=0$ b) $B=0,E\ne 0$
c)$B=0,E=0$ d) $B\ne 0,E\ne 0$

• A. a, b, c are true
• B. b, c, d are true
• C. a, b, d are true
• D. a, c, d are true

Answer 1

The correct option is D a, c, d are true

If $B=0$, $E=0$, then no force.

If $B=0,E\ne 0$ then electric force will act and cause an acceleration.
If $B\ne 0,E\ne 0$ then magnetic force and electric force might be balancing.
If B $\ne 0,E=0$ then speed will be same but velocity may not change if $B$ acts along the velocity.