School of Physics Lecture Demonstration Manual

El-6 Biot's Apparatus

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


To demonstrate that the charge resides on the surface of a statically charged conductor.



Click on pictures to enlarge.

Biot's Apparatus

Biot's Apparatus Diagram


A spherical conductor A mounted on an insulating stand is charged by contact in the normal way. Two uncharged hemispherical metal caps B which just fit over A are placed in position and then removed.

Tests with the proof plane show that the charge resides only on the outside of the metal caps B.

This experiment demonstrates that the charge on a proof plane can be transferred to an electroscope by having the proof plane touch the inside of the cylinder connected to an electroscope.

Safety notes

Electrical safety 


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