AP Physics C: Electricity and Magnetism Practice Quiz: Redistribution of Charge Between Conductors
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Test your understanding with short quizzes. This quiz has 10 questions to check your progress.
Question 1 of 10
All Questions (10)
A) Electrons flow from the neutral sphere to the positive sphere.
B) The neutral sphere remains electrically neutral.
C) The positively charged sphere becomes neutral.
D) Both spheres become negatively charged.
Correct Answer: A
The positively charged sphere has a higher electric potential than the neutral sphere. When they touch, charges redistribute to equalize their potentials. This is achieved by negative charges (electrons) moving from the object at lower potential (the neutral sphere) to the object at higher potential (the positive sphere).
A) The net charge on each conductor.
B) The electric field strength at the surface of each conductor.
C) The electric potential at the surface of each conductor.
D) The surface area of each conductor.
Correct Answer: C
The fundamental condition for electrostatic equilibrium for conductors in electrical contact is that charge will redistribute until all points on the surfaces of the connected conductors are at the same electric potential.
A) It has a net positive charge.
B) It is a perfect electrical insulator.
C) It can absorb or provide charge without changing its zero electric potential.
D) It repels any nearby charges.
Correct Answer: C
Ground is defined as an idealized reference point that is maintained at zero electric potential. It can act as a virtually infinite source or sink for charge, meaning it can accept or supply a large amount of charge without its own potential changing.
A) Positive
B) Negative
C) Neutral
D) It depends on how long it was grounded.
Correct Answer: A
This process describes charging by induction. The negative rod repels electrons in the sphere. When grounded, these repelled electrons have a path to flow away from the sphere to the ground. Removing the ground connection traps the remaining deficit of electrons, leaving the sphere with a net positive charge.
A) Positive charges flow from the conductor to the ground.
B) Electrons flow from the ground to the conductor.
C) The conductor's positive charge is transferred to the wire.
D) No charge will flow as ground is neutral.
Correct Answer: B
The positively charged conductor is at a high positive potential relative to the ground's zero potential. To equalize potentials, negative charges (electrons) are attracted from the ground and flow to the conductor, neutralizing its positive charge until the conductor also reaches zero potential.
A) To push positive charges from the conductor into the ground.
B) To create a potential difference that draws electrons from the ground onto the conductor.
C) To transfer positive charge directly to the conductor.
D) To make the entire conductor have a uniform positive potential.
Correct Answer: B
The external electric field from the positive rod attracts free electrons. When the conductor is grounded, it is connected to a reservoir of charge at zero potential. The attraction from the rod creates a potential difference that pulls electrons from the ground onto the conductor.
A) Sphere A and Sphere B have the same amount of charge.
B) Sphere A and Sphere B have the same surface charge density.
C) Sphere A and Sphere B have the same electric potential.
D) The electric field inside Sphere A is greater than inside Sphere B.
Correct Answer: C
Regardless of the size, shape, or final charge distribution, the defining characteristic of conductors in electrical contact at equilibrium is that their surfaces are at the same electric potential. The charge will distribute unevenly to ensure this condition is met.
A) One conductor is completely discharged.
B) The net charge of the system is zero.
C) The surfaces of the conductors are at the same electric potential.
D) The conductors have equal and opposite charges.
Correct Answer: C
Charge flows between conductors in contact due to a difference in electric potential. This flow ceases when the potential is equalized everywhere on the surfaces of the connected conductors, at which point the system reaches electrostatic equilibrium.
A) Touch the conductor with a negatively charged rod.
B) Bring a positively charged rod near the conductor and then ground the conductor.
C) Bring a negatively charged rod near the conductor, but do not ground it.
D) Touch the conductor to ground without any other objects nearby.
Correct Answer: B
To induce a negative charge, one must attract electrons from the ground. Bringing a positively charged rod near the neutral conductor will attract electrons. Grounding the conductor provides a path for electrons to flow from the ground onto the conductor. Removing the ground first, then the rod, will trap this excess negative charge.
A) Because the Earth is a perfect insulator and cannot store charge.
B) Because the Earth's magnetic field cancels out its electric potential.
C) Because the Earth is so large that adding or removing charge has a negligible effect on its overall potential.
D) Because the Earth has a perfectly uniform distribution of charge on its surface.
Correct Answer: C
The concept of ground having zero potential is an idealization based on the Earth's massive size. It can absorb or provide a very large amount of charge relative to typical laboratory-scale objects without its electric potential changing in any significant way. Therefore, it serves as a stable reference.