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Model No. ES-9080
Basic Electrostatics System
25
to move the connecting cable from the 3000 V to the 2000 V slot.
Examine the charge density near the center of one capacitor plate.
How does the charge vary with the voltage? Repeat with 1000
VDC.
3B.4: V Measured, C Variable, Q Constant
1.
Figure 3.4 shows the
equipment set up.
The Parallel Plate
capacitor is
connected to the
electrometer and the
electrometer is
grounded to earth.
The voltage source
will be used to only momentarily charge the capacitor.
2.
With the plate separation at 2 mm, charge the plates by
momentarily connecting them across the voltage source, set at 30
V. Adjust the scale sensitivity of the electrometer so that the
initially charged plates represent a meter reading of about 1/5 scale.
3.
Increase the plate separation and note the electrometer’s readings at
various separations. How does the potential vary with capacitance?
NOTE:
An alternative method is to charge one of the spheres and then
transfer some charge to the capacitor. The charge, however, will not be
as high.
Procedure 3C: Dielectric Coefficients
The dielectric coefficient is the dimensionless factor by which the
capacitance increases (relative to the value of capacitance before the
dielectric) when a dielectric is inserted between the plates. It is a
fundamental property of the dielectric material and is independent of
the size or shape of the capacitor. Table 3.1 on page 28 lists the
dielectric coefficients of some common materials.
The ideal procedure to measure would be to simply slip a piece of
dielectric material between a set of charged capacitor plates and then
note the changes in potential. However, sliding a dielectric between the
plates of the capacitor when they are too close together can generate a
significant static charge that will alter the measurements. Hence, it is
best to proceed as follows:
Figure 3.4: Demonstration Setup
N
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