Ohm’s Law 1
Name ______________________________________________ Date _________ Period ______
Resistance and Ohm’s Law
Purpose
After reading the lab, create your own purpose below:
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Materials
Wires
Bulbs
Bulb Sockets
Digital Multimeter with Test Leads
Foil
Wood
Plastic
Metal
Paper Clips
“D” batteries
Procedure (Don’t copy the steps. Just describe each part in your own words)
Part 1 – Measuring Resistance
1. Set the multimeter to measure resistance (Ω).
2. Use the two leads to test the insulators/conductors from the “Electricity” lab. Record their
resistance in Table 1. (Note: If the meter reads “1” or “oL”, there is too high a resistance
to be measured. Record this as “Infinite” in Table 1.)
3. Set the potentiometer to 10. Attach the two leads to opposite ends of the potentiometer.
Record the resistance in Table 2.
4. Repeat step 3 for settings of 8, 6, 4, 2 and 0 on the potentiometer.
Part 2 – Voltage and Resistance
5. Build a circuit with a battery pack, a potentiometer (set to 10), a switch, and a bulb.
6. Use the multimeter to measure the total battery voltage by touching the leads to the wires
connected to the pack. Record above Table 3.
7. Open the switch, move the red lead of the multimeter to “A”, and turn the multimeter dial
to measure direct current. Measure the current of the circuit by touching the leads to each
side of the switch. Record the current and a bulb brightness observation in Table 3.
8. Repeat step 7 for settings of 8, 6, 4, 2, and 0 on the pot.
Part 3 – Determining Resistance
9. Rebuild the circuit with a battery pack, switch, and a color-coded mystery resistor. Leave
the switch open.
10. Measure and record the current in Table 4.
11. Replace the resistor with one of a different color and repeat step 10.
Ohm’s Law 2
Data
Part 1 – Measuring Resistance
Table 1 – The Resistance of Objects
Object
Conductor or Insulator?
Resistance (Ω)
Foil
Cardboard
Paperclip
Straw
Nail
Pen Tube
Rubber Band
Table 2 – Potentiometer Resistance
Resistance (Ω)
Pot Setting
10
8
6
4
2
0
Part 2 – Voltage and Resistance
Battery Voltage = _________________ V
Pot Setting
10
8
6
4
2
0
Table 3 – Pot Settings and Circuit Current
Bulb Brightness
Measured Current (A) Calculated Current (A)
Ohm’s Law 3
Part 3 – Determining Resistance
Resistor Color
Table 4 – Mystery Resistors
Calculated Resistance (Ω)
Measured Current (A)
Green
Blue
Red
Calculations (show one sample calculation)
1. In part 2, use the battery voltage, resistance of the pot at each setting (from Table 2), and
Ohm’s law to calculate the current at each setting. Record in Table 3.
2. In part 3, use the battery voltage (From part 2) and Ohm’s Law to calculate the resistance
of each mystery resistor. Record in Table 4.
Questions
Part 1 – Measuring Resistance
1. What relationship did you notice between the resistance and whether a material was a
conductor or insulator?
2. What happened to the resistance as you increased the number on the dial of the
potentiometer? What do you think the numbers mean?
Part 2 – Voltage and Resistance
3. Draw a diagram of the circuit you built.
4. What happened to the current when you adjusted the pot setting?
Part 3 – Determining Resistance
5. Which of the resistors had the highest resistance? How did you know?
Conclusion
Based on your calculations from parts 2 &3, does this experiment prove Ohm’s law? Explain
why there may be differences between the calculated and measured currents in step 2.