School of Physics Lecture Demonstration Manual

El-2 The Electrophorous - Charging by Induction

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

Aim

To demonstrate charging by induction using the electrophorous.

Apparatus

Diagrams

Click on pictures to enlarge.

The Electrophorous

Electrphorous Diagram

Videos

The Electrophorous

Description

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 

Maintenance 

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