Monthly Archives: January 2019

Electric Field near a Pointy Conductor

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.

PointyConductor

PointyConductor

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.