Question

A strong magnetic field is applied on a stationary electron. Then the electron:
A. Moves in the direction of the field
B. Remains stationary
C. Starts spinning
D. Moves opposite to the direction of the field

Answer 1

Hint: A stationary electron in a constant magnetic field does not experience the Lorentz Force (F), regardless of how strong the magnetic field may be. Regardless of the external field’s orientation, there will be attraction force to both external magnetic poles, cancelling each other so the net force on the electron will always be zero, causing the electron to remain stationary.

Complete step by step answer:
Given a stationary electron
A magnetic field is a vector that describes the magnetic influence of electric charges in relative motion and magnetized materials. A charge that is moving parallel to a current of other charges experiences force perpendicular to its own velocity.
A stationary electron cannot make current. As the electric field is steady, there is no magnetic field.
The magnetic field B is defined in terms of force on moving charge in the Lorentz force law. The SI unit of the magnetic field is Tesla.
The magnetic force on a moving charge is given by
\[\overrightarrow {\text{F}} = \overrightarrow {\text{q}} \left( {\overrightarrow {\text{v}} \times \overrightarrow {\text{B}} } \right)\]
Where \[\overrightarrow {\text{q}} \]is the charge, \[\overrightarrow {\text{v}} \]is the velocity and\[\overrightarrow {\text{B}} \]is the magnetic field.
As the electron is stationary, therefore velocity
 \[\therefore \]\[\overrightarrow {\text{v}} = 0\]
As\[\left( {\overrightarrow {\text{v}} \times \overrightarrow {\text{B}} } \right)\]is the vector cross product which insures that the force will be perpendicular to both the velocity and to the magnetic field. So if the velocity and field are in the same direction, there will be no magnetic field.
\[\therefore \overrightarrow {\text{F}} = 0\].
So, electrons will remain stationary.

Note:
We can answer this question in a different way that is, an electron can be imagined as a bar magnet (a magnetic dipole), let say the external magnetic field lines from the left situated North Pole: N-S orientation will cause the electron to take S-N orientation, and vice versa. Regardless of the external field’s orientation, there will always be attraction force to both external magnetic poles, cancelling each other so the net force on the electron will always be zero, causing the electron to remain stationary.