Download Ohms(Lim Aceved0)

Jared Acevedo & Kenny Lim
Physics 102 Lab #3: Ohm’s Law
February 14, 2006
Abstract
The purpose of this lab is to construct a series circuit, a parallel circuit and a
combination parallel-series circuit choosing three different resistance values for each
resistor while setting the power supply to 6 Volts. Building these different circuits will
allow us to verify Ohm’s Law: V=IR.
Equipment
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Voltmeter (digital)
Ammeter (digital)
Resistors (decade boxes)
D.C. Power Supply
6 Connecting Wires
Procedure
1. In order to build the first circuit (Series) three resistors (decade boxes) were
connected to one another in a series, while the Power Supply was connected to
the first resistor and the third resistor in the series.
2. The first resistor was set to 100Ω, the second resistor in the series was set to
200Ω, and the third was set to 300Ω.
3. The Power Supply was turned on and set to 6 volts.
4. The current was measured by replacing a wire from the Voltmeter and set to
DCA.
5. The voltage was measured across each resistor.
6. The parallel circuit was made by placing the conducting wires from the Power
Supply on one resistor, then on the second, then on the third.
7. Once all wires were connected steps 2-5 were performed..
8. In order to create a series-parallel circuit the first two resistors were created in
a parallel arrangement as above, while the third was placed in series with the
other two bulbs.
9. Once all wires were connected steps 2-5 were once again performed
Data
Please see Excel Spreadsheet for data.
Calculations
1. Theoretical current for series circuit
V = IR ; I = V/R
V = 6V
Rtotal = 100Ω + 200Ω + 300Ω = 600Ω
I = 6V / 600Ω = 0.01 A
2. Theoretical total resistance and current.
V = IR
V = 6V
1/Rtotal = (1/100Ω) + (1/200Ω) + (1/300Ω)
Rtotal = 54.54
I = 6V / 54.54Ω = 0.11 A
3. Theoretical currents.
I = V/R
V1 = 2.680V
V2 = 3.261V
V3 = 3.270V
I1 = 2.680V / 100Ω = 0.0268 A
I2 = 3.261V / 200Ω = 0.0163 A
I3 = 3.270V / 300Ω = 0.0109 A
Slope for series circuit graph.
Slope = Rise / Run
Slope = (2.945 – 2.033) / (300 – 200) = 0.01 Slope is the value for the current.
Slope for parallel circuit graph.
Slope = (0.10 – 0.02) / [(1 / 54.54) – (1 / 300)] = 5.33 Slope is the value for the voltage
Graphs
Please see Excel Spreadsheet (chart 1 and 2) for graphs.
Error Analysis
The weakness in this experiment that can cause an error is some of the
equipments we used in the lab and how we handled or used the equipment during the
experiment. First of all, errors can occur from the uncertainty of the equipments we used
for determining the currents and voltage (digital voltmeter & ammeter). Also connecting
wires can cause a little error on current flow due to certain inhibitions. Some of the
potential errors can be made by misplacing connecting wires, resistors or equipments to
measure the voltage and current.
% Error on series voltage = [|6.000V – 6.007V| / 6.000V] X 100 = 0.12%
% Error on parallel voltage = [|6.00V – 5.92V| / 6.00V|] X 100 = 1.33%
% Error on combination current = [|0.0109A – 0.0100A| / 0.0109A] X 100 = 8.3%
Questions
1. What can you say about the sum of the voltage drops in circuit 1?
The voltage drops in circuit 1 will add up to approximately the total voltage
(6V) as a result of the conservation of energy. In our circuit, V1=1.029 +
V2=2.033 + V3=2.945 Vtotal= 6.00.
2. What can you say about the sum of the currents through the resistors in
circuit 2?
The current sum that enters from point A must equal the total current leaving
that point. Therefore the total current must be approximately equal to the sum
of the individual currents. In our circuit I1=.05A + I2=.04A + I3=.02A = Itotal
=.11A.
3. Construct a graph for each circuit. Look for obvious linear relationships
and calculate the slopes of these lines.
See Graphs on Excel Spreadsheet. In the series circuit a linear
relationship between the slope of Volts vs Ohms or V/R is equal to the current
(I) from V=IR. In the parallel circuit, the linear relationship between the slope
of Amps vs 1/Ohms or A/(1/Ω) is equal to the total voltage from V=IR.
4. Construct a table, subdivided into three parts, where every experimental
value is compared with its theoretical value.
See table on Excel Spreadsheet.
Conclusion
In this experiment, we determined the current and the voltage of the series,
parallel and series-parallel combination circuit with the pre-determined resistance value.
This is done to study the relationship between the current, voltage and resistance and to
prove the Ohm’s law (V=IR). In the series circuit, the current stayed constant and as
voltage increases, resistance increased as well. In the parallel circuit, voltage stayed the
same so therefore, the current and resistance have an inverse relationship. As the current
goes up, resistance goes down.
Grade: 98/100