PHY 242 Laboratory for 8/27/98

Electric Field Mapping

NOTE: The air exchanger is out, so we will postpone the Electrostatics lab until next week. I will give the necessary background for the Electric Field Mapping exercise at the beginning of the lab session.

Following the instructions provided with the Overbeck Field Mapping Apparatus, each group will map the equipotential lines of at least three patterns including the plane-plane and the Faraday ice pail. Space equipotential points close enough together to insure that an accurate equipotential line can be sketched through the points. Each member of the group should have a copy of the point maps.

Report:

  1. Sketch the equipotential lines and indicate the potential of each. Sketch the electric field lines of force for each map. The lines of force should be perpendicular to conductors and to the equipotential lines at all points. Take care in making your sketch!
  2. Select and label two unique points on one of the maps and estimate the strength of the electric field at each those points using DV = Ed. Explain your calculations.
  3. Using the estimated value of E or V nearby, estimate the charge residing on the point conductor on one of the maps.
  4. Using the electric field, show in detail (in a separate sketch) how the charge is distributed on the conducting surfaces of one of the maps.

  5. Answer the following questions:
    1. Why must the lines of force be perpendicular to the surface of any conductor with a static charge distribution?
    2. Is it possible for equipotential lines to cross? Is it possible for lines of force to cross? Explain.
    3. For the plane-plane pattern, approximately by what percentage does the field strength differ between the center and edge of the plates along the bisector? Explain your estimate.
    4. For the Faraday ice pail pattern, comment on the field strength inside the pail. What can you say about the charge distribution on the pail?