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.
- The Electrophorous
- Cats fur
Click on pictures to enlarge.
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.