Question

A proton with a velocity in the positive x-direction enters a region where there is a uniform magnetic field B in the positive y-direction. You want to balance the magnetic force with an electric force so that the proton will continue along a straight line.
The electric field should be in the:

a)neg y direction

b)neg x direction

c)postive x direction

d)postive z direction

e)negative z

Answer 1

Answer:

Positive z direction.

Explanation:

The magnetic force acting on the electron is given by the formula as :

$F=q(v\times B)$

q is the charge on proton

v is the speed of proton

B is the magnetic field

It is mentioned that the proton is moving with a velocity in the positive x-direction. The uniform magnetic field B in the positive y-direction such taht,

q = +e

v = vi

B = Bj

$F=e(v\ i\times B\ j)$

Since, $i\times j=k$

$F=(evB)\ k$

So, the magnetic force acting on the proton in positive z axis. Hence, the correct option is (d) "positive z direction".