Physics Dept. Demonstration Manual

DEM07 - Electric Field Demonstration, "Seed in Oil"


To show an analogy of the electric field or the electric lines of force surrounding conductors of selected geometry.

  • Electric field "platform"
  • single point pattern
  • two points (opposite charge) pattern
  • hollow sphere (section) pattern
  • coaxial pattern
  • parallel plates pattern
  • plate and points pattern
  • Wimshurst machine
  • Transformer Oil
  • Grass seed
  • Leads
  • 15 cm Petri dish and cover


The "platform" with the bottom half of a Petrie Dish is placed on the O.H. Projector, and connected to the electrodes of the Wimshurst Machine. About 1 cm depth of oil is added, and the desired conductor shapes are plugged in and immersed in the oil. Grass seed is sprinkled lightly and evenly on the oil. The O.H. Projector is focussed on the layer of seeds. The Wimshurst Machine is then cranked one or two times (only), setting up a potential gradient between the conductors. The seeds become charged and align along the electric lines of force.