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
neg y direction
neg x direction
postive x direction
postive z direction
negative z

Answer 1

Answer:

Negative z-direction

Explanation:

First of all, we need to understand the direction of the magnetic force on the proton. This can be determined by using the right hand rule. So we have:

- index finger: direction of the proton, positive x-direction

- middle finger: direction of magnetic field, positive y-direction

- thumb: direction of the force, positive z-direction

In order to balance this magnetic force, the electric force must act in the opposite direction (negative z direction). Since for a proton (positive charge) the force and the electric field have same direction, it means that the electric field must also be in the negative z direction.