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Physics 102
Ohm’s Law
Elizabeth Silva and Maria Zavala
January 30, 2006
Abstract:
The purpose of this lab is to test the current intensity and potential differences when
conductors of different resistance are connected in varies circuits.
Equipment:
● Digital voltmeter
● Digital Ammeter
● Resistors (decade boxes)
● Variable D.C. power supply
● Wires
Procedure:
1. Choose three different values for R1, R2, and R3.
2. Set the resistors to these set values. (resistance should be greater than 20 ohms,
but the same order of magnitude/
3. Set the power supply to 6V.
4. Construct a series circuit with the three resistors.
5. Measure the current through and voltage across each resistor.
6. Construct a parallel circuit with the three resistors.
7. Measure the current through and voltage across each resistor.
8. Measure the current between the positive side of the power supply and R1.
9. Construct a circuit with R1 in series with a parallel branch containing R2 and R3.
10. Measure the current through and voltage across each resistor.
Data:
Series Circuit:
R1
R2
R3
Resistance
30Ω
60Ω
90Ω
Voltage
0.937 V
2.222 V
2.853 V
Current
(I)
0.04 A
0.05 A
0.06 A
Voltage
5.93 V
6.07 V
5.95 V
Current
(I)
02.1 A
02.2 A
02.2 A
Parallel Circuit:
R1
R2
R3
Resistance
30Ω
60Ω
90Ω
One Circuit ( one series and 2 parallel):
Resistance Voltage Current (I)
R1
30Ω
2.685 V
0.17 A
R2
60Ω
3.44 V
0.20 A
R3
90Ω
3.33 V
0.20 A
Current (I) between positive side and
R1:
0.4 A
Initial Voltage (V) of power
supply:
6.08 V
Initial current (I) of power
supply:
2.15 A
Calculations:
For Series Circuit:
The formula to find the theoretical total resistance is as follows.
RT = R1 + R2 + R3
RT = 30Ω + 60Ω + 90Ω = 180Ω
The formula to find the total theoretical current is as follows.
IT = VT / RT
IT = 6.0 V / 180 Ω = 0.03 A
The formula to find the total theoretical voltage across each resistor is as follows.
V1T = IT * R1
V1T = 0.03 A * 30Ω = 0.9 V
The formula to find the % error of voltage and current is as follows.
[(THEOR – ACTUAL) / THEOR] x 100%= % error
The calculations for the voltage % error in the circuit series.
V1 = 4.4% error
V2 = 23.3%
V3= 5.6%
The calculations for the current for the circuit series.
I = 66.7%
For Parallel Circuit:
The formula to find the theoretical total resistance is as follow.
1 / RT = 1/30 + 1/60 + 1/90 = R=16.36 Ω
The formula to find the total theoretical current is as follows.
I THEORETICAL = V / Rtotal = 6.0V / 16.36 Ω= 0.37A
The calculation for the voltage and current % error in the parallel series is as follows.
V% error= 0.3%
I1% error= 950 %
I2% error= 2100 %
I3% error= 3043 %
For 1 Series and 2 Parallel Circuit:
The formula to find the theoretical total resistance is as follows.
R23 = 1 / R23 = 1/R2 + 1/R3 = 1/60 + 1/90 =1/36 = 36Ω
RTOTAL = R 123 = R1 + R23 = 30+36 = 66 Ω
The formula to find the total theoretical current is as follows.
I THEORETICAL = VTOTAL / R123 = 6V/ 66A = 0.09 A
The formula to find the total theoretical voltage across each resistor is as follows.
V23 = I THEO X R23 = 0.09A X 36Ω = 3.24V
V1THEO = 0.09 A X 30 OHMS = 2.7 V
VTOTAL = V1 + V23 = 2.7 V +3.24 V = 5.94V
The calculations for the voltage and current % error in the series and parallel circuit.
V% error= 2.4%
I1% error= 88.9 %
I2% error= 77.8 %
I3% error= 77.8%
Graphs:
See attached
Error Analysis:
The percent error calculations indicate an extremely high percent error for the one circuit
with one in series and 2 two in parallel. The high percentage of 3043%, 950%, and
2100% may be due to calculation errors or an error when obtaining the data. There may
have also been error in the way the circuit was constructed.
Questions:
1. What can you say about the voltage drops in Circuit 1?
The voltage for a series is not suppose to be constant, so it has to fluxuate.
The initial voltage is 6V, then it drops down to 0.937V. The dramatic drop may be
resistance that is encountered.
2. What can you say about the sum of the current through the resistors?
The sum of the current remains consistent throughout the circuit. This is evident
for all circuits in this experiment.
3. Construct a graph for each circuit plotting every V(I) point. Look for obvious linear
relationships and calculate the slopes of theses lines.
4. Construct value (What you measured) is compared with its theoretical value (what you
calculate with Ohm’s Law).
Series Circuit
Parallel Circuit
One Circuit
(1 Series,2
Parallel)
V1
V2
V3
V1
V2
V3
V1
Theoretical
Values
0.9V
1.8V
2.7V
6V
6V
6V
2.7V
Experimental
Values
0.937V
2.222V
2.853V
5.93V
6.07V
5.95V
2.685V
V2
V3
3.24V
3.24V
3.44V
3.33V
Conclusion:
This experiment helped us understand Ohms Law. That is the relationship between
resistance, current, and voltage. The calculated percent errors were 3043%, 950%, and
2100% for the current on the parallel circuit. The percent error for the mixed circuit was
2.4%, 88.9%, 77.8%, and 77.8%.
You are missing the graphs and the slopes
Grade: 85/100