Module 23: Electric Potential Energy and Electric Potential

How are electric field lines related to equipotential surfaces?

Electric field lines are always perpendicular to equipotential surfaces and point toward locations of lower potential.

If there is a system with two electrons and a proton, can the electric potential energy of the system be exactly zero?

Yes, it could be zero if they were arranged properly.

If there is a system with a proton and an electron, can the electric potential energy of the system be exactly zero?

No, it will be negative no matter how they are arranged.

Which of the following is a good description of the electric force between stationary charged objects?

The electric force between stationary charged objects is a conservative force for which there is a corresponding potential energy.

If a proton is moved a certain distance directly opposite an external electric field, what can we say about the change in the electric potential energy of the system?

The electric potential energy of the system will increase.

If an object with charge -3 nC moves from a location that has a potential of -20 V to a location with a potential of -10 V, what has happened to the potential energy of the system?

The potential energy of the system has decreased by DELTA U= - (10V)(3nC)

If an object with charge +2 nC moves from a location that has a potential of 20 V to a location with a potential of -10 V, what has happened to the potential energy of the system?

The potential energy of the system has decreased by DELTA U= -(30V)(2nC)

A cube of copper and a sphere of aluminum are both positively charged and connected by a wire. What do the two conductors have in common?

They both have the same electric potential.

Consider a point 1 cm away from an electron with nothing else nearby. What expression could represent the electric potential at that location?

V= - 1/4pi e0 times the absolute value of qe / 0.01m

Every point on an equipotential surface ______.

has the same electric potential

If an electron is moved in a direction perpendicular to an equipotential surface, ______.

it will be moving either in the same or exactly opposite direction as the electric field at that location

When an electron approaches a positively charged nucleus, ______.

the electric potential energy of the system decreases while the potential at the electrons location increases

As we consider various points that are all on the same equipotential surface near some distribution of charge, ______.

the electric potential is the same at every point

If an electron moves in a direction perpendicular to an equipotential surface, ______.

the potential it experiences must change

Which of these is a good description of the difference between electric potential energy and electric potential?

Electric potential energy is a property of a system of multiple charges while electric potential is a property of a location in space near a charge distribution.

Consider two point charges, A and B, separated by a distance, d. How would we find the total electric potential energy of this arrangement?

Calculate one electric potential energy for the pair.

Consider three point charges, A, B, and C, arranged in an equilateral triangle, with distance d on each side. How would we find the total electric potential energy of this arrangement?

Find the three electric potential energies (one for each pair) and add them up.

If there is a system with two electrons, can the electric potential energy of the system be exactly zero

No, it will be positive no matter how they are arranged.

An arbitrarily shaped piece of conductor is given a net negative charge and is alone in space. What can we say about the electric potential within the conductor? Assume that the electric potential is zero at points that are very far away from the conductor.

The electric potential in the conductor will be negative and constant throughout the conductor.

An arbitrarily shaped piece of conductor is given a net positive charge and is alone in space. What can we say about the electric potential within the conductor? Assume that the electric potential is zero at points that are very far away from the conductor.

The electric potential in the conductor will be positive and constant throughout the conductor.

If a proton is moved a certain distance directly opposite an external electric field, what can we say about the change in the electric potential it experiences?

The electric potential it experiences will increase.

If an electron is moved a certain distance directly opposite an external electric field, what can we say about the change in the electric potential it experiences?

The electric potential it experiences will increase.

When two electrons are 1 cm apart, what expression could represent their electric potential energy?

U = 1/4pi e0 times (the absolute value of qe)2/ 0.01m

If an electron is moved a certain distance directly opposite an external electric field, what can we say about the change in the electric potential energy of the system?

he electric potential energy of the system will decrease

As we consider various points that are all on the same equipotential surface near some distribution of charge

the electric potential is the same at every point, but the electric potential energy is different at every point