Coulomb's law/ image charge

Principle

A small electrically charged ball is positioned at a certain distance in front of a metal plate lying at earth potential. The surface charge on the plate due to electrostatic induction together with the charged ball forms an electric field analogous to that which exists between two oppositely charged point charges. The electrostatic force acting on the ball can be measured with a sensitive torsion dynamometer.

Benefits

• Experimental visualisation of a fundamental principle of electrodynamics
• Supplies non-hazardous high voltage
• Very sensitive measurement of the acting force

Tasks

1. Establishment of the relation between the active force and the charge on the ball.
2. Establishment of the relation between force and distance, ball to metal plate.

Learning objectives

• Electric field
• Electric field strength
• Electric flux
• Electrostatic induction
• Surface charge density
• Dielectric displacement
• Electrostatic potential