UNIVERSITY OF MASSACHUSETTS DARTMOUTH
COLLEGE OF ENGINEERING
EGR 101 INTRODUCTION TO ENGINEERING THROUGH APPLIED SCIENCE I
CAPACITORS
INTRODUCTION
In this lab you will measure some properties of capacitors on a breadboard and then
simulate the behavior of a capacitor in a circuit.
Part 1 Capacitance Measurements
Capacitors have the ability to temporarily store charge and then, under the right
conditions, release it back into the circuit. A measure of a capacitor’s ability to store
charge is its capacitance. Today you will measure the capacitance of individual and
combinations of capacitors.
You will be given 3 capacitors.

Plug each individually into your DMM and record the measured capacitance in a
table similar to Table 1. Be sure to note and record the markings on each
capacitor so you know which is which.

Second, connect the 3 capacitors in series on your breadboard. Use 2 wires,
one at each end to connect the capacitors to your DMM. Record the total
capacitance in Table 1.

Third, connect the 3 capacitors in parallel on your breadboard. Again use 2 wires
to connect the capacitor network to your DMM. Record the total capacitance in
Table 1.
Table 1 Equivalent capacitance in series and parallel.
Capacitor(s)
Measured Value (μf)
Predicted Value (μf)
N/A
N/A
N/A
Series combination
Parallel combination
Part 2 Multisim Circuit
Consider the circuit shown in Figure 1.
Figure 1 A capacitor charging/discharging circuit.
Assume that the switch has been in position 2 for a long time and is then thrown to
position 1 as shown (this ensures that there is no charge on the capacitor). The battery
voltage is now applied to the capacitor via resistor R1, and the capacitor voltage will
change according to
 t 

 
 

R
C
vc (t )  Vs 1  e  1  




and eventually reach VS. The current through resistor R1 becomes equal to 0, and the
circuit will remain in this condition.
 For C = 1μF, select R1 so that it will take 12 ms to fully charge the capacitor (5 )
(item 1).
 Determine from the above equation how long it takes to reach 50% of Vs (item
2).
If the switch is moved to position 2, the circuit becomes
Vc
Figure 2 The switch is in position 2 to discharge the capacitor.
The charged capacitor is now connected to ground via resistor R2, and it will discharge
according to
 t 

 
R
C
vc (t )  Vse  2 
and eventually reach 0 volts.
 For C = 1μF, Select R2 so that it will take 7.45 ms to discharge the capacitor
(item 3).
 Determine from the equation how long it takes to reach 50% of Vs (item 4).
CONNECTION TO THE OSCILLOSCOPE
An oscilloscope is required in order to view these charging and discharging
characteristics. The capacitor voltage can be observed on one channel of the
oscilloscope as shown below.
Figure 3 An oscilloscope connected to monitor the capacitor voltage.
 Verify the charging time by measuring on the oscilloscope the time it takes to
fully charge the capacitor (item 5), and compare the reading with your derived
value in item 1.
 Verify on the scope the time it takes the voltage to reach 50% of Vs (item 6).
 Measure the voltage across R1 when the capacitor is fully charged (item 7).
 Verify the discharging time by measuring on the oscilloscope the time it takes to
fully discharge the capacitor (item 8), and compare the reading with your derived
value in item 3.
 Verify on the scope the time it takes the voltage to reach 50% of Vs (item 9).
 Measure the voltage across R2 when the capacitor is fully discharged (item 10).
DELIVERABLES
Each team will submit the following:
 Table 1.
o Observation about capacitors in series.
o Observation about capacitors in parallel.
 A printout of Multisim charging/discharging characteristics of the circuit as
observed on the oscilloscope.
 Detailed account of all 10 items.