Basic Electrostatics System
Model No. ES-9080
18
!
Demonstration 2: Charge Distribution
Equipment Setup
Introduction
The purpose of this demonstration is to investigate the way charge is
distributed over a surface by measuring variations of charge density. A
charged surface will be sampled with a proof plane. The proof plane
will then be inserted in the Faraday Ice Pail to measure the charge. By
sampling different sections of the surface, the relative charge density
can be observed. For example, you may find that the amount of charge
on two equal sized regions on the surface of a conductor may differ in
magnitude or even in sign. This occurs for non-uniform charge
distribution. Alternately, you may observe that everywhere on the
surface the charge has the same magnitude and sign. This occurs for
uniform charge distribution.
An important aspect of measuring charge distributions is charge
conservation. The proof plane removes some charge from the surface it
samples. If the proof plane is grounded after each measurement, the
surface will be depleted of charge with consecutive measurements.
However, by not grounding the proof plane (and by not letting it touch
Equipment Required:
Electrometer (ES-9078)
Faraday Ice Pail (ES-9042A)
Electrostatic Voltage Source (ES-9077)
Proof Planes
Conductive Spheres, 13 cm (ES-9059B) (2)
Test leads
Earth ground connection (patch cord)
pail
earth ground
charged
sphere
sampling
sphere
DC voltage source*
power cord
and VDC source
ground VDC source
share common
to earth or to shield
ground
Figure 2.1 Demonstration Setup
electrometer
electrometer, shield
*
An earth ground for the system is obtained through the DC voltage source wall-mount power.