Ohm’s Law in Parallel Circuit Lab
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Objectives: The purpose of this lab exercise will be to reinforce concepts learned in the classroom
segment of Electricity/Electronics. These concepts include, in parallel connected circuits current is
additive, voltage drop is the same through-out the circuit, and total resistance is found by adding the
reciprocal of the sum of the reciprocals of the individual legs of the circuits. Students will gain
experience in building prototype circuits, making measurements and proving experimentally
fundamental electricity principles. Remember from the previous lab, students learned that current
must be measured in series with the load. In this lab, lamps have been replaced with a very basic
solid state component know as an LED.
Procedure:
A. Parallel connected resistance
1. Read the entire lab exercise before coming to class to complete the lab assignment.
2. Record the rated resistance on the schematic diagram and in the rated resistance row
of the chart.
3. Measure the resistance of each of the resistors individually and record the
measurements in the space provided in the chart.
4. Connect the resistors in parallel according to the schematic diagram, measure the total
resistance for the parallel connected resistances and record the measurement in the
Rmeas. row and the Rtotal column.
5. For RTcalc. use the formula for parallel resistance.
R1
R2
R3
R4
value
value
value
value
R1
Rrated
Rmeas.
Rcalc.
R2
R3
R4
Rtotal
Ohm’s Law in Parallel Circuit Lab
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Procedure:
B. Parallel voltage drops
1. Read the supplement containing the information regarding the LED. Keep in mind that
LED’s are polarity sensitive devices and must be connected correctly in order to be
operational.
2. Construct the circuit at the top of the next page using jumper wires between each of the
LED’s as indicated by the schematic diagram. Set the voltage for the value outlined
during the classroom introduction for this lab exercise.
3. For each measurement observe the correct meter polarity.
4. Measure the voltages across the LED’s and record the measurements in the spaces
provided.
5. Measure the currents between the indicated points with the jumper wire removed and
record the current measurements in the space provided in the chart.
6. For IT below add all of the measurements from the third column and record this as IT.
(ITcalc. = IK-I + IL-G + IM-E + IN-C)
7. Be sure to answer the questions at the end of this exercise as this is an excellent way to
check an individual’s understanding.
O
J
H
V1
F
D1
D
D2
D3
D4
value
I
A
EJ-I
EH-G
EF-E
ED-C
B
G
K
L
EN-O
IK-I
EN-O
IL-G
switch open
EA-B
switch open
ET
E
C
M
IA-B
switch open
IA-B
switch closed
IM-E
ITcalc.
IN-C
PT
N
Ohm’s Law in Parallel Circuit Lab
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Questions:
1. What has been proven about voltage in a parallel circuit?
2. Describe what happened to the circuit the instant one of the jumper wires was removed for
measuring current?
3. How would you connect LED’s for maximum light output? Explain your answer.
4. Explain why your house could not/ should not be wired in series.
Ohm’s Law in Parallel Circuit Lab
Page 4 of 4
5. Describe what you know about current in parallel.
6. How much voltage did one LED drop with this circuit and how does it compare with the series
circuit voltage drop across one LED?
7. What were the color bands on R2?
8. What were the color bands on R4?
9. How many paths for current are there in the circuit with the LED’s?
10. What can be noted about the voltage drop across LED #3 when compared to ET?