OHM’S LAW - CIRCUITS
INTRODUCTION
The purpose of this lab is to prove ohm’s law and understand series and parallel direct current circuits.
EQUIPMENT LIST
1. 12 volt direct current (DC) power supply
2. Various DC bulbs with sockets (12V and 3V (two cell flashlight bulbs))
3. VOM or device(s) to measure voltage and current
4. Constant 500 to 1K ohm resistance source (Wire coil, wire wound or carbon resistor)
5. Assorted wires
OBJECTIVES
Upon successful completion of the lab the student will:
· prove Ohm’s law
· demonstrate and understand the principles of resistance
· explain series and parallel circuits
· demonstrate the use of a VOM or other measuring devices
· use the VOM to check for continuity.
NEEDED EQUATIONS
V = IR
P = VI
EXAMPLE CALCULATIONS
Determine the slope of a voltage verses current graph. The slope will be the resistance.
DETAILED PROCEDURE
1. / Connect power supply to the resistor.
2. / Make sure the power supply is off and has a 0 voltage output.
3. / Place the VOM in voltage DC mode.
4. / Connect the VOM across the resistor.
5. / Check connections with an instructor and then turn on power supply.
6. / Adjust the dial until 1 volt is measured on the VOM
7. / Turn off the power supply without changing voltage dial setting.
8. / Set the meter in DC current mode.
9. / Insert the meter in series with the resistor and power supply.
10. / Turn the power supply back on and record the current.
11. / Repeat steps 4 through 10 in one volt increments, recording your results for each increase in voltage.
Volt / Current / Power
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
12. / Make a graph of voltage vs. current and determine the slope of the line. The slope of the line equates to the resistance.
13. / Calculate the power for each of the voltage settings.
Resistance of a light bulb
14. / Replace the resistor with a 12V light bulb.
15. / Repeat steps 2-11.
Volt / Current / Power
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
16. / Graph the voltage vs. current. The graph should not be linear because the resistance changes as the filament of the bulb heats up.
DC Series Circuit
17. / Connect three, 3V light bulbs in series.
18. / Connect the power supply to the circuit.
19. / Turn on the power supply and adjust the power supply until illumination of the bulbs can be seen.
20. / Unscrew one bulb and observe what happens.
21. / Replace the bulb with a 12V bulb. Observe what happens.
22. / Instructor might demonstrate constant current in the circuit.
DC Parallel Circuit
23. / Connect three, 12V light bulbs in parallel.
24. / Connect the power supply to the circuit.
25. / Turn on the power supply and adjust the power supply until illumination of the bulbs can be seen.
26. / Unscrew one bulb and observe what happens.
27. / Check continuity of 3V bulb to verify it is operational.
28. / Replace the bulb with a 3V bulb. Observe what happens.
29. / Measure continuity of 3V bulb to verify open condition.
30. / Instructor might demonstrate constant voltage in the circuit.
SAMPLE DATA
In the simple DC circuit the current will be measured in milliamps and must be converted to amps. In the parallel circuit, expect the 3V bulb used in part 5 to burn out.
RECOMMENDED SOFTWARE PACKAGES TO USE
MS Word
MS Excel
Ohm’s Law – Circuits (Alternative Lab)
INTRODUCTION
The purpose of this lab is to prove Ohm’s Law and to understand series and parallel DC circuits.
EQUIPMENT LIST
1. 12 volt DC power supply
2. Various resistors and conductors
3. VOM or device(s) to measure voltage, resistance, and current
OBJECTIVES
Upon successful completion of the lab the student will:
ü Prove Ohm’s Law
ü Demonstrate and understand principles of resistance
ü Explain series and parallel circuits
ü Demonstrate the use of the VOM
EQUATIONS
V=IR
P=VI
EXAMPLE CALCULATIONS
Determine the slope of a voltage verses current graph. The slope will be the resistance.
DETAILED PROCEDURE
Simple DC circuit
1. Connect the power supply and resistor.
2. Make sure that the power supply is off and has a 0V output.
3. Place the VOM in the DC voltage mode.
4. Connect the VOM across the resistor
5. Check connections with an instructor and then turn on the power supply.
6. Adjust the dial until 1V is measured on the VOM.
7. Turn off the power supply without changing the setting.
8. Set the meter in DC current mode.
9. Insert the meter in series with the resistor and power supply.
10. Turn the power supply back on and record the current.
11. Repeat steps 4 through 10 in one volt increments, recording your results for each increase in voltage.
Voltage / Current / Power1
2
3
4
5
6
7
8
9
10
12. Make a graph of voltage vs. current and determine the slope of the line. The slope of the line equates to the resistance. (place the graph on the back of this sheet)
13. Calculate the power for each of the resistance settings.
14. Connect 3 resistors in series.
15. Connect the power supply to the circuit.
16. Turn on the power supply and adjust the power supply to 9V.
17. Measure the voltage across all three resistors.
18. Measure the voltage across each resistor individually.
R1 / R2 / R3 / TotalVoltage
19. Does the sum of the voltages across the resistors equal the total voltage? ______
20. Ask your instructor to demonstrate constant current in series circuits.
21. Connect the three resistors in parallel.
22. Turn on the power supply and adjust it to 9V.
23. Measure the Voltage across each resistor.
24. What can you say about voltage in a parallel circuit?