Answer:
(A) electric and gravitational fields but not magnetic fields.
Explanation:
Let's analyze the effect produced by each of the three fields on the stationary electron:
- Gravitational force: the gravitational force exerted on the electron by a gravitational field is
where
m is the mass of the electron
g is the strength of the gravitational field
Since the mass of the electron m is non-zero, the electron experiences a gravitational force.
- Electric field: the electric force exerted on the electron by an electric field is
where
q is the charge of the electron
E is the magnitude of the electric field
Since the charge q of the electron is non-zero, the electron experiences an electric force.
- Magnetic field: the magnetic force exerted on the electron by a magnetic field is
where
q is the electron charge
v is the velocity of the electron
B is the magnitude of the magnetic field
is the angle between the direction of v and B
Since the electron is stationary, we notice that the velocity is zero: v=0, therefore the magnetic force is zero as well.
Therefore, the correct answer is
(A) electric and gravitational fields but not magnetic fields.