School of Physics Lecture Demonstration Manual

El-2 The Electrophorous - Charging by Induction

Published: Tuesday 14 March 2006 - Updated: Thursday 31 March 2011


To demonstrate charging by induction using the electrophorous.



Click on pictures to enlarge.

The Electrophorous

Electrphorous Diagram


The Electrophorous


The Electrophorous consists of a flat metal disc A, fitted with an insulating handle H, a flat disc B of an insulating material (ebonite) resting on an earthed metal sole S.

The plate B is rubbed with the cats fur and acquires a charge; B acquires a negative charge. A is now placed on B and since neither A or B are perfectly flat, contact is limited to a very few points. The surfaces are separated therefore by a thin layer of air. A has charges induced on it.

If A is now earthed by touching while it is still resting on B, electrons will flow from it to earth leaving a nett positive charge on A which can be used as a source of charge.

The above procedure can be repeated many times since no charge has been removed from B.

Safety notes

Electrical safety 


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