Which of the following fields push on a stationary electron? (a) electric and gravitational fields but not magnetic fields. (b) gravitational fields but not electric or magnetic fields. (c) electric, magnetic, and gravitational fields. (d) magnetic and gravitational fields but not electric fields.

(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.