Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

# Discussion Questions - Electric Fields

A In the definition of the electric field, does the test charge need to be 1 coulomb? Does it need to be positive?
B Does a charged particle such as an electron or proton feel a force from its own electric field?
C Is there an electric field surrounding a wall socket that has nothing plugged into it, or a battery that is just sitting on a table?
D In a flashlight powered by a battery, which way do the electric fields point? What would the fields be like inside the wires? Inside the filament of the bulb?
E Criticize the following statement: "An electric field can be represented by a sea of arrows showing how current is flowing."
F The field of a point charge, |E|=kQ/r2, was derived in the self-check above. How would the field pattern of a uniformly charged sphere compare with the field of a point charge?
G The interior of a perfect electrical conductor in equilibrium must have zero electric field, since otherwise the free charges within it would be drifting in response to the field, and it would not be in equilibrium. What about the field right at the surface of a perfect conductor? Consider the possibility of a field perpendicular to the surface or parallel to it.
H

Compare the dipole moments of the molecules and molecular ions shown in the figure.

I Small pieces of paper that have not been electrically prepared in any way can be picked up with a charged object such as a charged piece of tape. In our new terminology, we could describe the tape's charge as inducing a dipole moment in the paper. Can a similar technique be used to induce not just a dipole moment but a charge?
J The earth and moon are fairly uneven in size and far apart, like a baseball and a ping-pong ball held in your outstretched arms. Imagine instead a planetary system with the character of a double planet: two planets of equal size, close together. Sketch a sea of arrows diagram of their gravitational field.

Last Update: 2009-06-21