Question

An electron is moving northward in a magnetic field. The magnetic force on the electron is toward the northeast. What is the direction of the magnetic field?
-up

-This situation cannot exist because of the relative orientations fo the velocity and force vectors

-down

-west

-south

Answer 1

To solve this problem we will use the vector concept given by the cross product between two perpendicular vectors and which results in a vector perpendicular to these two. From the definition of the Magnetic Force we have to

$\vec{F}=q(\vec{v}\times\vec{B})$

From the property of cross product the magnetic force should point in the direction perpendicular to the plane containing the vectors v and B.

The direction of velocity is north, and the direction of the magnetic force is northeast.

This cannot be the case, as the direction of magnetic force is not perpendicular to the direction of velocity of the charge.

Therefore the correct option for the direction of the magnetic field is "This situation cannot exist because of the relative orientations of the velocity and force vectors"