Varying degrees of uniformity of the electric field are worth considering. Parallel plate capacitors have a nearly perfect uniformity (except at the edges). Spherical and cylindrical conductors have fields which are highly concentrated near the conductor. But they are the same in all radial directions. A pointy conductor has charge and field concentrations which are high near the pointy areas. The purpose the Pointy Conductor simulation is to demonstrate this non-uniformity near sharp points. A complete worksheet is available to guide students in this exploration. Note the following:
- The E-fields are concentrated near points, and equipotentials are closely-spaced
- The E-field strength is proportional to the density of the E-lines
- The charge density at a spot on the conductor surface is proportional to the E-field there
- The voltage gradient is proportional to the E-field strength
- Pointier shapes have larger non-uniformities and higher E-fields.
In order access the oblong conductor website, use the following information, and choose
Study the E-field at a Point
Student Worksheet Downloadable Word Doc
We used the following word document as a lab procedure in the PHY112 and PHY131 classes.
Points for Discussion
- A lightning rod is a pointy conductor. How does a lightning rod prevent destructive lightning strikes?
- How does a very high electric field cause an avalanche of current flow (“Avalanche Breakdown”).
- Why are large rounded shapes used in the vicinity of very high voltages in machines that are used to accelerate charged particles?
- E-field lines must approach a conducting surface at a right angle.