# OHM'S LAW LAB

## Gunn Physics

PURPOSE:

The purpose of this lab is to investigate the relationship between the three variables involved in Ohm's Law - Current, Voltage and Resistance.

MATERIALS:

• Circuits Experiment Board
• D-Cell
• Wire
• Digital Multimeter (DMM)
• Resistors

PROCEDURE:

1. Choose one of the resistors that you have been given. Using the chart at the bottom of this page or your notes, decode the resistance value and record that value in the first column of the Data Table.

2. Construct the circuit above, leaving the wire between the resistor and the battery unconnected. Have the instructor check your wiring before going on.
3. Set the DMM to the 20 MA range, noting that the red lead should be connected to the plug on the DMM designated for "MA" or "A". The black lead should always be connected to the "COMMON" plug. When your circuit has been approved, connect the remaining wire and read the current that is flowing through the resistor. Record this value in the second column of the Data Table. Note that the decimal point is for MA or milliamps - 0.001 amps.
4. Now replace the original resistor with the remaining resistors, one at a time, each time recording the resistance value and the current you measured.
5. When you have completed measuring all of the currents, disconnect the meter and connect the circuit shown below. Change the meter to the 2VDC scale (or 2000 mV) and move the red lead to the plug on the meter that indicates "V". Measure and record the voltage across the resistor for each of the resistors. (On the 2000 mV scale, the decimal point is for millivolts.)

6. When finished making measurements, turn the meter off, secure all of the resistors by placing at least one end of each in a spring, and disconnect the wire(s) from the battery. Process the data you've obtained. The results of this experiment are important and will definitely be covered on any quizes, etc.

DATA TABLE:

 Resistance W Current A Voltage V Voltage/Resistance V/W

ANALYSIS:

1. For each of your sets of data, calculate the ratio of Voltage/Resistance. Compare the values you calculate with the measured values of the current.

2. Construct a graph of Current (vertical axis) vs Resistance.

DISCUSSION:

1. Why do you think there was an unusual occurence in the voltage readings you obtained with different resistors?

2. From your graph, what is the mathematical relationship between Current and Resistance (for a constant voltage)?

3. Ohm's Law states that current is equal to the ratio of voltage/resistance. Does your data concur with this?

4. What were possible sources of experimental error in this lab? Would you expect each to make your results larger or to make them smaller?

REFERENCE: