!
Model No. ES-9080
Basic Electrostatics System
23
Procedure 3B: Measuring C, V and Q for a Parallel Plate
Capacitor
The purpose of the experiments listed in this part is to qualitatively
study the relationship between C, V, and Q for the parallel plate
capacitor. Values read by the electrometer are to be used as relative,
comparative measurements. The electrometer can be connected to a
computer and used with a
ScienceWorkshop
£
interface to obtain a
graphical display of information.
3B.1: V Measured, Q Variable, C Constant
1.
Figure 3.2 below shows the equipment set up. The Parallel Plate
capacitor is connected to the electrometer. The electrometer is
grounded to earth. One of the spheres is connected to the voltage
source, set at 2000 VDC. Take care to place the capacitor sufficiently
far away from the sphere and the voltage source, to prevent it from
being charged by induction.
2.
Press the
ZERO
button to remove any residual charge from the
electrometer and the plates of the capacitor.
3.
Set the plate separation to about 2 mm. Use a proof plane to transfer
charge from the charged sphere to the capacitor plates. The charge
is transferred merely by touching the proof plane to the sphere and
then to one capacitor plate. If you always touch the sphere and the
capacitor plate at the same place, equal amounts of charge will be
transferred each time.
Question: Why is it sufficient to touch only one plate of the
capacitor?
CE
V V
E
–
V
----------------------
C
=
;
power
basic variable
capacitor
2000
VDC
proof
plane
Figure 3.2: Demonstration Setup
sphere
to earth
ground
electrometer