fields pre lab

Field Mapping Pre-lab Exercise

last updated Sept. 24, 2002

You should be familiar with most the equipment we are using in this lab. Most of the equipment we have used in previous labs. The remainder is very easy to use and requires very little explanation. I assume that you have studied electric fields in the lecture part of the course.

In the field mapping lab, we will be plotting the electric field of three charge configurations: 1) the electric dipole, 2) a cylindrical capacitor, and 3) a parallel plate capacitor. This exercise is designed to help you recall what an electric field is and to give you the thoretical electric field lines and equipotential lines for the three configurations. Note: the theoretical field lines and equipotential lines given are your "known" for this lab.

1. Electric Fields: Electric Fields are related to the Coulomb force (i.e. like charges repel, opposite charges attract). Field lines tell you the direction of the force on a positive "test" charge. The electric force is related to the electric field by the equation F = qE, where q is your test charge. If you drew an arrow indicating the force on this "test" charge at all points in space you would get a drawing of the electric field lines. You can try this out with the applet at: http://www.colorado.edu/physics/2000/applets/nforcefield.html

(The picture above is a screen shot of the applet. Note that the "test" charges here are negative! This is not the convention that most physicists use, but you get the idea.)

2. Equipotential lines: Equipotential lines indicate the points in space where the potential is the same. Another words, these are all the points where it takes the same amount of energy to bring in a positive "test" charge in from far away. An important feature of equipotential lines is that they are perpendicular to electric field lines.

3. Electric Fields and Equipotentials in our lab: (Note: I drew all of the following with my applet at http://www2.hawaii.edu/~jmcfatri/labs/FieldDisplay.html and I added nicer looking charges and arrows in Photoshop.)

Configuration	Electric Field Lines	Electric Potential
Electric Dipole
Cylindrical Capacitor
Parallel Plate Capacitor

Questions:

No questions to turn in. But do try the applets! Please print this page out so that you can have it in lab.