• Electric potential

Topics:  Electric field, flux, charge distribution.

Pre-requisite skills: Right-hand rule.

Approximate completion time:  Under an hour.

Provide sufficient detail to verify that the assignment was completed in a meaningful manner.

Applet by Wolfgang Christian

When drawing electric field lines from a plot of equipotential lines, a common question is "How far apart should the electric field lines be spaced?"  One rule of thumb that can be used is to use a circle whose diameter reaches from one equipotential line to the next, as shown in the below figure.  (This rule of thumb requires that the equipotential lines are incremented by constant steps in value, which is the case for the above applet.)  The electric field lines (shown in blue) are drawn so as to perpendicular to the equipotential lines and, at the same time, touch the circle.

1.  If equipotential lines are spaced close together, is this indicative of a strong or weak electric field?

2.  Examine the spacing between the equipotential lines for two different regions around the charges.  Using your answer to Question 1, which regions in space correspond to a relatively strong electric field?

3.  Pick a region near the top-left or bottom-right of the applet, far from the two charges.  Using the displayed values of two equipotential lines and the perpindicular distance between the lines, calculate the electric field strength in this region.    Do the same for the region directly between the two charges.  Do your answers agree with your answer to Question 2?

4. You will notice that the charge values are not given in the above applet.  Describe the polarity (negative or positive) of each charge.  Explain your reasoning.  (Be sure to indicate the location of each charge as you dicuss it.)