Dynamics Track
Inclined Plane
Momentum

Capacitor
Plate Sep
Plate Sep/Volt
Dielectrics

Circuits
Ohms Law
Series/Parallel

Wave Tank
Freq/Wavelength
Two Pt Interf.

Optical Bench
Refraction
Focal Length

Circuit Experiment Board

Verification of Ohm’s Law

Purpose:

In this lab, you will verify Ohms Law for four different resistors.   You will measure the true resistance of each resistor and the voltage applied to each resistor.   You will then calculate the predicted current through each resistor.   Finally, you will measure the actual current through each resistor to verify (or disprove!) Ohm’s Law.

Equipment:

• Digital Multimeter
• Circuit Experiment Board
• Jumper Wires
• Resistors (already on the Ex. Board)

Cautions:

This equipment is delicate.   Everything should go together with the lightest of touches.   Do not force anything!

Measuring Resistance:

1. Make sure that the black and red leads are in the black and red sockets of the multimeter.
2. Turn the multimeter on (button on the upper right) and make sure that it is set to read DC.   Numbers will appear on the display.   If you see “AC” on the display, push the AC/DC button to make the “AC” go away.
3. Turn the dial to “2k” on the “Ω” scale   This sets up the meter to measure resistances up to 2000Ω in thousands of ohms (kΩ).   Expect the value you read to be less than 1.0.
4. Touch the probes to both ends of the leftmost resistor and note the meter reading This measures the true resistance of this component.
5. Multiply this value by 1000.   This converts the reading from kΩ to Ω.
6. Enter the resistance value in the table under R-1.
7. Repeat steps 4-6 for the other three resistors.

Measuring Voltage

1. Connect a wire from the “+” terminal of the battery to the upper end of the leftmost resistor Simply slip the bare end of the wire between the spring coils to make the connection.   Do not pry the coils apart!
2. Connect a wire from the “-” terminal of the battery to the lower end of the leftmost resistor This completes the circuit through the leftmost resistor.
3. On the multimeter, turn the dial to “2” on the “V” scale. Now the meter will measure voltages from 0-2V.
4. Touch the probes to both ends of the leftmost resistor and note the meter reading.   This measures the true voltage across the resistor
5. Record the voltage reading under the “R-1” column.
6. Remove both wires from the circuit.   This disconnects the resistor from the voltage source.
7. Repeat steps 4-6 for the other three resistors.

Measuring Current:

1. On the multimeter, turn the dial to “20m” on the “A” scale.   This is the 20 milliamperes scale.   You will have to multiply the readings by 1000 to get a value in amperes.
2. Move the red multimeter lead to the “A” socket on the multimeter.   This sets the meter up to read current from 0-20mA.
   
   CAUTION:   NEVER put the multimeter leads directly on a voltage source when the meter is set up to read current.   This will damage the meter!   Follow the next instructions exactly!
   
3. Connect a wire from the “+” terminal to the top of the leftmost resistor.
4. Touch one multimeter lead to the “-“ terminal of the battery.
5. Touch the other multimeter lead to the bottom of the leftmost resistor and note the meter reading.
6. Divide the meter reading by 1000 and record it in the R-1 column of the table
7. Disconnect the wire from the “+” terminal and the resistor
8. Repeat steps 3-7 for the remaining three resistors.

Cleaning Up:

1. Move the red multimeter lead from the “A” socket to red socket.
2. Turn off the multimeter.
3. Make sure that everything is in the same place as you found it.
   
   You may return to the classroom.

Calculating:

1. For each resistor, divide its voltage figure by its resistance figure to obtain the calculated current.   Record this figure at the bottom of each resistor’s column.

Data analysis:

Does your data support Ohm’s Law?   Did the calculated currents match the measured currents?   If the values were not close, analyze the reason for this and check your calculations carefully.