PASCO EM-8622 BASIC ELECTRICITY - Manual (Page 27)

23
012-04367E Basic Electricity
Purpose
The purpose of this lab will be to determine how capacitors behave in R-C circuits. The manner in
which capacitors combine will also be studied.
Procedure
➀
Connect the circuit shown in Figure 8.1, using a 100-K
Ω
resistor and a 100-µF capacitor. Use one
of the spring clips from the transistor socket as a “switch” as shown. Connect the VTVM so the
black “ground” lead is on the side of the capacitor that connects to the negative terminal of the
battery and set it so that it reads to a maximum of 1.5 V DC.
➁
Start with no voltage on the capacitor and
the wire from the “switch” to the circuit
disconnected. If there is a remaining
voltage on the capacitor, use a piece of
wire to “short” the two leads together,
draining any remaining charge. (Touch
the ends of the wire to points B and C as
shown in Figure 1 to discharge the
capacitor.)
➂
Now close the “switch” by touching the
wire to the spring clip. Observe the
voltage readings on the VTVM, the
voltage across the capacitor. How would
you describe the manner in which the
voltage changes?
➃
If you now open the “switch” by removing the wire from the spring clip, the capacitor should
remain at its present voltage with a very slow drop over time. This indicates that the charge you
placed on the capacitor has no way to move back to neutralize the excess charges on the two
plates.
➄
Connect a wire between points A and C in the circuit, allowing the charge to drain back through
the resistor. Observe the voltage readings on the VTVM as the charge flows back. How would
you describe the manner in which the voltage falls? (It would be reasonable to sketch a graph
showing the manner in which the voltage rose over time as well as the manner in which it fell over time.)
➅
Repeat steps 3-5 until you have a good feeling for the process of charging and discharging of a
capacitor through a resistance.
➆
Now repeat steps 3-5, this time recording the time taken to move from 0.0 volts to 0.95 volts while
charging, t
C
, and the time taken to move from 1.5 volts to 0.55 volts while discharging, t
D
. Record
your times along with the resistance and capacitance values in Table 8.1 at the top of the back page.
Experiment 8: Capacitors in Circuits
EQUIPMENT NEEDED:
– Vacuum Tube Voltmeter (VTVM) or Elec-
trometer (ES-9054B) or Digital Multimeter
(DMM) that has an input impedance of 10 M
Ω
or greater.
– Circuits Experiment Board
– Capacitors, Resistors
– Wire Leads
– D-cell Battery
– Stopwatch or timer with 0.1 sec resolution.
V
Resistor
C
B
➤
A
Capacitor
“Switch”
+ -
Figure 8.1