If e represents the magnitude of the proton charge, what minimum magnitude of the magnetic field

Question

A proton traveling with speed v enters a uniform electric field of magnitude E, directed parallel to the plane of the page, as shown in the figure. There is also a magnetic force on the proton that is in the direction opposite to that of the electric force.

If e represents the magnitude of the proton charge, what minimum magnitude of the magnetic field could balance the electric force on the proton?

(A) E/v 

(B) eE/v 

(C) vE 

(D) eE 

(E) evE

Answer 1

The correct option is: (A) E/v 

Explanation:

F_e = F_b

Eq = qvB

E = vB 

B = E/v