!
Model No. ES-9080
Basic Electrostatics System
31
2.
Set up the circuit shown in Figure 4.1, where the resistor and the
capacitor are connected in series to the voltage source, set at 30
VDC. The electrometer output goes to one of the analog channels
of
ScienceWorkshop
. Use a single-pole double-throw switch.
3.
Set up your experiment display in the computer to plot voltage vs.
time. (Refer to the steps listed above for correcting the electrometer
readings.)
4.
With the switch open, press start to begin collecting data. Throw
the switch to position A to begin charging the capacitor. Observe
the behavior of the voltage on the screen.
5.
When the charge in the capacitor has reached the value of the
source (30 VDC), flip the switch to position B to begin discharging
the capacitor. Observe the behavior of the voltage in the screen.
6.
You may want to try the experiment with different values of R and
notice the differences in charging time.
Analysis:
When a capacitor is charged through a resistor from a DC power
supply, the charge on the capacitor and the voltage across the capacitor
increase with time. The voltage,
V
, as a function of time is given by
V
=
V
0
(1 -
e
t/RC
) where V
0
is the charging voltage.
After a time
t = RC
(one time constant), the voltage across the
capacitor has increased to 63% its maximum value (
V
= 0.63
V
0
at t =
RC ).
Figure 4.1: Experimental Setup and Circuit
red lead
black lead
signal output
electrometer
double-throw
s
witch
signal
interface