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Ohm’s Law
Name: ………………………………………… Class: ……………….. Date: ………………..
OBJECTIVES
 Determine the mathematical relationship between current, potential difference, and
resistance in a simple circuit.
Figure 1
HYPOTHESIS
MATERIALS
Ammeter
Adjustable 12 volt DC power supply
Connected wires
Two resistors (about 10 and 50 )
PROCEDURE
1. With the power supply turned off, connect the power supply, 10  resistor, wires and
ammeter as shown in Figure 1. Take care that the positive lead from the power supply
and the red terminal from the ammeter are connected as shown in Figure 1.
Note: Attach the red connectors electrically closer to the positive side of the power
supply.
2. Turn on the power supply. Slowly increase the potential to 2 V, 4 V and so on. Record
the readings of ammeter and power supply in table 1.
3. Calculate the resistance for each time by using ohms law: V = IR
4. Plot a single graph of potential vs. current.
a. Plot Voltage on the y-axis (the vertical axis)
b. Plot Current on the x-axis (the horizontal axis)
5. Calculate the slope of the graph.
DATA TABLES
RESISTOR 1
Voltage
Current
Resistance
(V)
(A)
(Ω)
RESISTOR 2
2
4
6
8
10
12
Voltage
Current
Resistance
(V)
(A)
(Ω)
ANALYSIS
Answer the following questions
1. What happened to the current as the voltage was increased? If the voltage is
doubled what happens to the current?
2. What was the shape of the graph you obtained? What kind of relationship exists
between voltage and current? How close is your y-intercept to zero?
3. How do the values of the constants you got in each of the above equations (in the
tables) compare to the value of the slope you calculated?
4. Compare the value of the slope to the actual value of the resistance. Calculate the
percentage error.
5. Do your resistors follow Ohm’s Law? How can you tell?
6. Write an equation for each resistor in the form Voltage = constant  current. (Use a
numerical value for the constant.)