Electric Potential III

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

The above applet depicts an unknown charge (shown in black) and a test charge (in red). Be sure to read the instructions if you are not fully aware of the operation of the applet.

1. Using the displayed value of the potential and location, calculate the unknown charge.

2. Is the unknown charge positively charged, or negatively charged? Explain.

3. In which direction does the electric field point?

4. Consider a point a radial distance r = 3 from the unknown charge. (Assume all units are SI.)

(a) Using Coulomb's Law and your previous answers, calculate the electric field strength at this point.

(b) Now using the value of the potential at this point, and the value of the potential a short distance from this point, calculate the electric field strength.

(c) Calculate a percent difference between the two answers. Is your answer to (b) reasonably close to your answer to (c)?

5. Using graph paper and the data displayed by the applet, draw a plot of the potential as a function of the radial distance from the charge. Describe your result and explain why it is expected given the mathematical relationship of the potential for a point charge. If the charge was oppositely charged, how would your plot be changed?

Helpful Resources

Electric Charges, Fields, and Potentials by Ian Littlewood.
The Physics Hypertextbook by Glenn Elert (see Electric Potential)
Electric Fields of a System of Charges by Angel Franco Garcia (in Spanish).
Book of Phyz - Motion by Dean Baird
Physlet Problems: Electric Potential by Wolfgang Christian
P10D - Electricity and Magnetism by Janak Sodha

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