University Physics Volume 2

# Conceptual Questions

University Physics Volume 2Conceptual Questions

### 7.1Electric Potential Energy

1.

Would electric potential energy be meaningful if the electric field were not conservative?

2.

Why do we need to be careful about work done on the system versus work done by the system in calculations?

3.

Does the order in which we assemble a system of point charges affect the total work done?

### 7.2Electric Potential and Potential Difference

4.

Discuss how potential difference and electric field strength are related. Give an example.

5.

What is the strength of the electric field in a region where the electric potential is constant?

6.

If a proton is released from rest in an electric field, will it move in the direction of increasing or decreasing potential? Also answer this question for an electron and a neutron. Explain why.

7.

Voltage is the common word for potential difference. Which term is more descriptive, voltage or potential difference?

8.

If the voltage between two points is zero, can a test charge be moved between them with zero net work being done? Can this necessarily be done without exerting a force? Explain.

9.

What is the relationship between voltage and energy? More precisely, what is the relationship between potential difference and electric potential energy?

10.

Voltages are always measured between two points. Why?

11.

How are units of volts and electron-volts related? How do they differ?

12.

Can a particle move in a direction of increasing electric potential, yet have its electric potential energy decrease? Explain

### 7.3Calculations of Electric Potential

13.

Compare the electric dipole moments of charges $±Q±Q$ separated by a distance d and charges $±Q/2±Q/2$ separated by a distance d/2.

14.

Would Gauss’s law be helpful for determining the electric field of a dipole? Why?

15.

In what region of space is the potential due to a uniformly charged sphere the same as that of a point charge? In what region does it differ from that of a point charge?

16.

Can the potential of a nonuniformly charged sphere be the same as that of a point charge? Explain.

### 7.4Determining Field from Potential

17.

If the electric field is zero throughout a region, must the electric potential also be zero in that region?

18.

Explain why knowledge of $E→(x,y,z)E→(x,y,z)$ is not sufficient to determine V(x,y,z). What about the other way around?

### 7.5Equipotential Surfaces and Conductors

19.

If two points are at the same potential, are there any electric field lines connecting them?

20.

Suppose you have a map of equipotential surfaces spaced 1.0 V apart. What do the distances between the surfaces in a particular region tell you about the strength of the $E→E→$ in that region?

21.

Is the electric potential necessarily constant over the surface of a conductor?

22.

Under electrostatic conditions, the excess charge on a conductor resides on its surface. Does this mean that all of the conduction electrons in a conductor are on the surface?

23.

Can a positively charged conductor be at a negative potential? Explain.

24.

Can equipotential surfaces intersect?

### 7.6Applications of Electrostatics

25.

Why are the metal support rods for satellite network dishes generally grounded?

26.

(a) Why are fish reasonably safe in an electrical storm? (b) Why are swimmers nonetheless ordered to get out of the water in the same circumstance?

27.

What are the similarities and differences between the processes in a photocopier and an electrostatic precipitator?

28.

About what magnitude of potential is used to charge the drum of a photocopy machine? A web search for “xerography” may be of use.