Ohm’s Law Lab (combo)

Name:Date:

Objective: Part I:To prove Ohm’s Law as it applies to resistors and to investigate the relationship between current, voltage and resistance. Also, observe the differences between a regular resistor and a light bulb.Part II: To investigate the relationship between resistance and length and area of a resistor.

Apparatus:Part I

Part II

Procedure:Part I:

  1. Build the circuit above. Note: You must have it wired correctly to obtain good data!
  2. When finished have Mr. Pagett check it out for errors
  3. Launch Capstone and select the graph (Voltage on y-axis and Current on x-axis)
  4. Press and hold Switch 1 for about 10 seconds. This will charge your capacitor.
  5. Start recording data.
  6. Press and hold Switch 2 while recording data.
  7. You should see the data graphed out on a V vs. I plot
  8. Highlight the straight line portion of the graph and do a linear fit on the data.
  9. The slope is the resistance of your resistor (record this data)
  10. Repeat the experiment to confirm results
  11. Repeat steps 1-8 for your other resistors and the light bulb.

Data: Part I Record the slope (“m”) of voltage versus current for each of the resistors.

Resistor / Slope / % error
10-ohm
25-ohm
Big Resistor
Lightbulb

Procedure: Part II:

1)Retrieve a can of play-dough and an analog voltmeter and ammeter

2)Take half of your play-dough and roll it out into a section that is about 10 cm long.

3)Hook your voltmeter in parallel with the play-dough and your ammeter in series creating a circuit with a switch and voltage source.

4)Depress your switch and measure the voltage and current in your circuit. Calculate the resistance.

5)Have Mr. Pagett decrease the voltage and repeat step 3.

6)Make another section of play-dough identical to the first. Replace your first section with the second and find its resistance.

7)Attach the sections of play-dough end to end and find the new resistance of your circuit.

8)Put your sections side by side and find the new resistance of your circuit.

Known-resistors

1)Take three resistors of the different resistances to use for this part.

2)Hook the 5 ohm resistor up into your circuit and measure the voltage and current.

3)Determine the resistance of the resistor and compare to the known value.

4)Repeat steps 2 and 3 with the other two resistors

Data: Part II

Play-dough

Step 3 -V=I = R =

Step 4 -V= I = R =

Step 5 -V= I =R =

Step 6 -V=I =R =

Step 7 -V=I =R =

Known resistors

5 ohm V=I = R = % error =

10 ohm V= I = R = % error =

25 ohm V= I =R = % error =

Questions:Part I

1)How does the slope of the plot of voltage versus current for the 10-ohm resistor compare to the resistance value?

2)How does the slope of the plot of voltage versus current for the 25-ohm resistor compare to the resistance value?

3)How does the slope of your big resistor compare to the known value?

4)Describe the plot of voltage versus current for the 10-ohm resistor (straight line, curved line, no relationship).

5)Describe the plot of voltage versus current for the 25-ohm resistor in comparison to the plot for the 10-ohm resistor.

6)How does the plot for the light bulb compare to the plot for either resistor?

7)Can you determine if the light bulb is an ohmic material? How?

8)What does the term non-ohmic mean?

9)What can you conclude about the relationship between current and voltage (in an ohmic material)?

10)What can you conclude about the relationship between current and resistance?

Part II:

1)How does the length of a conductor affect its resistance?

2)How does the cross-sectional area of a conductor affect its resistance?

3)The strength of the current in a circuit varies directly as ______and inversely as the ______. This is known as ______Law.

4)What are two other factors governing the resistance of materials other than those in questions 1 and 2.

5)If an ammeter records 8 A and a voltmeter records 1.1 V, what is the resistance?

6)What voltage is required to cause 12 A to flow through a resistance of 7.2 ohms?

7)What current will flow through a resistance of 11 ohms when the voltage is 2.8 V?

8)If you wanted to double the current flowing through your circuit what are the two things you could change?

Conclusion: