Question

If a proton,neutron and electron are placed in a magnetic field then which particle will experience zero force?

(A)Proton and electron 
(B) Neutron and proton
(C) Electron and neutron 
(D) Proton, neutron and electron

Answer 1

The neutron will experience zero force. If we assume that the particles are motionless, all 3 will experience zero force.

Explanation:

The neutron does not interact with magnetic fields regardless of conditions discussed below that may or may not cause a force on electrons and protons.

The proton and electron will experience zero force IF they are motionless in the magnetic field or if the velocity, `v`, and magnetic field, `B`, are parallel.

Charges, protons or electrons, with a velocity vector that is not parallel with the magnetic field will experience a force deflecting its path. The formula relating the force, charge and its velocity, and magnetic field is

`vecF = q*vecv " "X" " vecB`

where the `X` indicates that a vector cross product is to be done. It is this force that allows an electric motor to work.

I just now noticed that the choices do not offer neutron only. If we assume that the question implies that the particles are motionless, then the correct answer is D.

I hope this helps,
Steve