Current Electricity-Ohm’s Law Lab
Lab Team (2)
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Safety and Equipment Precautions!
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Plug in your power supply and use ONLY the D.C. terminals of the power source, NOT the A. C. terminals.
DO NOT touch wires together when the power supply is on.
DO NOT leave the circuit with the power supply on for long periods of time! The resistors get VERY hot
and may fry!
You must disconnect ALL wires from the resistor BEFORE you measure the Resistances of the resistors!
R=V/I
or
Procedure
In this lab, you will construct a simple circuit using a single resistor, then use a Multi-Meter to
measure the current (I) through the resistor, to measure the potential difference (V) across the resistor.
You will then calculate the Resistance of each resistor using Ohm's Law (R=V/I) in your simple circuit.
1. Using your circuit board, wires, power supply, create a complete simple circuit using ONE RESISTOR.
Follow the diagram or ask Mr. Putnam to check your connections before you continue.
2. Your Digital Multi-Meter can be used to determine Voltage across the resistor, Current through the
resistor and the Resistance of the resistor.
YOUR MULTI-METER MUST HAVE A DIFFERENT SETTINGS FOR EACH MEASUREMENT
AND
MUST BE PROPERLY MEASURED FOR VOLTAGE, CURRENT AND RESISTANCE!
TO TEST VOLTAGE…
Measure ACROSS THE RESISTOR
& set the Multi-meter to the
20V DC setting with probe wires
plugged in the multi-meter diagram
as shown.
TO TEST CURRENT…
Measure IN SERIES WITH THE
WIRE & set Multi-meter to the
10A DC setting with probe wires
plugged in the multi-meter diagram as
shown.
TO TEST RESISTANCE…
Measure ACROSS THE RESISTOR,
set Multi-meter to the 200 
setting with probe wires plugged in
the multi-meter diagram as shown.
ALWAYS measure
with the wires
leading to the
resistor
REMOVED!
Part A-Finding Resistance
1. Select Resistor-R1 on your circuit board and create a simple circuit using the alligator clip wires from the
white box.
2. Turn on the power supply and record the Voltage and Current through your resistor.
3. Measure the Resistance across your resistor with the multi-meter. Be certain to unplug the power supply
BEFORE measuring this value or you WILL blow a fuse!
4. Complete Table A.
Table A
Voltage (V)
Current (I)
Calculated
Resistance ()
R=V/I
Measured
Resistance ()
% Error
%E=CR-MR/MR
Resistor-R1
Part B-Finding Voltage
1. Select Resistor-R3 on your circuit board and create a simple circuit using the alligator clip wires from the
white box.
2. Turn on the power supply and record the Current through your resistor.
3. Measure the Resistance across your Resistor with the multi-meter. Be certain to unplug the power supply
BEFORE measuring this value or you WILL blow a fuse!
4. Complete Table B.
Table B
Current (I)
Measured
Resistance ()
Calculated
Voltage (V)
R=V/I
Measured
Voltage (V)
% Error
%E=CV-MV/MV
Resistor-R3
Part C-Finding Current
1. Select Resistor-R5 on your circuit board and create a simple circuit using alligator clip wires from the
white box.
2. Turn on the power supply and record the Voltage across your resistor.
3. Measure the Resistance across your Resistor with the multi-meter. Be certain to unplug the power supply
BEFORE measuring this value or you WILL blow a fuse!
4. Complete Table C.
Table C
Resistor-R5
Voltage (V)
Measured
Resistance ()
Calculated
Current (I)
R=V/I
Measured
Current (I)
% Error
%E=CC-MC/MC
Part D-Finding Resistance Graphically (Creating a graph of Ohm’s Law!)
1. Select Resistor-R2 on your circuit board and create a simple circuit using the alligator clip wires from the
white box.
2. Turn on the power supply and record the Voltage and Current through your resistor.
3. Now CHANGE the Voltage to a different setting on the Power supply. DO NOT turn the Power supply up
to a maximum! The fuse WIL blow and the Resistor will get hot! As long as the Voltage setting is
DIFFERENT from the previous value, that is acceptable. Repeat for 5 different Voltage settings.
4. Fill out the Table & create an Excel Graph of Voltage (V) vs. Current (I) & display the trendline equation.
(y-axis)
(x-axis)
5. Find the Resistance of your Resistor using your graph! Write the Resistance value on your graph.
Voltage (V)
Current (I)
Conclusions
1. Draw a Simple Circuit with the following conditions…
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…a 10Resistor
…an Ammeter reading 2A placed correctly in order to measure the current in the resistor.
…a Voltmeter placed to read the voltage across the Resistor.
…a Voltmeter placed to read the voltage across the battery.
…a Voltmeter placed to read the voltage across a section of wire in the circuit.
A. _______ = Voltmeter reading (resistor)
A
B. _______ = Voltmeter reading (battery)
C. _______ = Voltmeter reading (wire)
D. _______ = Total Current (entire circuit)
E. _______ = Total Resistance (entire circuit)
__________ 2. Your graph illustrates what Law of Electricity?
___________________ 3. If the values (V, I or R) found in your experiments DID NOT follows Ohm's Law
exactly, explain what may have been the source for errors. (Misreading the multi-meter is NOT an answer!)