EXPERIMENT OHM'S LAW
Reference: Alexander, Charles K. and Matthew Sadiku, Fundamentals of Electric Circuits, 5th Edition, McGraw Hill 2012
Objective:
The purpose of this laboratory exercise is to verify Ohm's law and to become familiar with the use of the laboratory equipment, particularly the power supply, breadboard, and digital multimeter.
Equipment:
• DMM ( Digital Multimeter)
• Breadboard
• Power Supply
• Resistors (1 kΩ,)
• Potentiometer
• Leads (2 pair)
• Alligator clips
Pre-lab Assignment:
1. Read section 2.2 of your textbook.
2. Complete the following Tables 1, 2, and 3 by using Ohm's law.
3. Then create a tabulation of the results in Excel and create three plots.
4. For table 1 create an x-y scatter plot of R versus I. The plot should have the current on the x-axis and the resistance on the y-axis. In Excel, right click the curve and add a trend line (power-series) and display the equation on the chart. Explain what you think this equation represents
5. For table 2, create an x-y scatter plot of current versus voltage. Determine the slope of the line and explain what you think this value represents.
6. For table 3, create an x-y scatter plot of voltage versus current. Determine the slope of the line and explain what you think this value represents.
During the laboratory experiment, the calculated data will be compared to the measured data found by using the digital multimeter. A key part of your laboratory report will include an error analysis of the calculated values versus the measured values.
The formula for percent error is,
(|theoreticd - measured| / theoreticd) x100
Your laboratory report should discuss the results found in detail including possible sources of error. The data table should look similar to the following data table.
Table 1: Variable Resistance
|
V (V)
|
I (mA)
|
R (k?) (calc)
|
R (k?) - potentiometer (meas)
|
R % error
|
|
10
|
10
|
|
|
|
|
10
|
9
|
|
|
|
|
10
|
8
|
|
|
|
|
10
|
7
|
|
|
|
|
10
|
6
|
|
|
|
|
10
|
5
|
|
|
|
|
10
|
4
|
|
|
|
|
10
|
3
|
|
|
|
|
10
|
2
|
|
|
|
|
10
|
1
|
|
|
|
Table 2: Ohm's Law (current)
|
V (V)
|
R (k?)
|
I (mA) (calc)
|
I (mA) (meas)
|
I % error
|
|
10
|
1
|
|
|
|
|
9
|
1
|
|
|
|
|
8
|
1
|
|
|
|
|
7
|
1
|
|
|
|
|
6
|
1
|
|
|
|
|
5
|
1
|
|
|
|
|
4
|
1
|
|
|
|
|
3
|
1
|
|
|
|
|
2
|
1
|
|
|
|
|
1
|
1
|
|
|
|
Table 3: Ohm's Law (voltage)
|
I (mA)
|
R (k?)
|
V (V) (calc)
|
V (V) (meas)
|
V % error
|
|
10
|
1
|
|
|
|
|
9
|
1
|
|
|
|
|
8
|
1
|
|
|
|
|
7
|
1
|
|
|
|
|
6
|
1
|
|
|
|
|
5
|
1
|
|
|
|
|
4
|
1
|
|
|
|
|
3
|
1
|
|
|
|
|
2
|
1
|
|
|
|
|
1
|
1
|
|
|
|
Procedure:
Part 1:
(a) Place one potentiometer on your breadboard
(b) Set the power supply to 10 V and place it across the center and side terminal of the potentiometer
(c) Set the DMM to read current and place it in series between the potentiometer and the power supply
(d) Adjust the potentiometer until the DMM reads 10 mA. Record the actual value of the current in your lab notebook.
(e) Remove the potentiometer and set the DMM to read resistance. Measure the value of the potentiometer across the terminals and record the value in your lab notebook.
(f) Repeat steps b - e for each current value given in Table 1.
Part 2:
(a) Place a 1 kΩ resistor on your breadboard.
(b) Measure the resistor and record the actual value and resistance in your lab notebook.
(c) Set the power supply to 10 V and place it across the resistor
(d) Set the DMM to read current and place it in series between the resistor and the power supply
(e) Measure the current through the resistor and record it in your lab notebook
(f) Repeat steps c - e for each voltage value given in Table 2
Part 3:
(a) Place a 1 kΩ resistor on your breadboard.
(b) Place the power supply across the resistor
(c) Set the DMM to read current and place it in series between the resistor and the power supply
(d) Vary the power supply voltage until the DMM reads 10 mA
(e) Record the power supply voltage
(f) Repeat steps d - e for each current value given in Table 3
Post-Lab Assignment:
(a) Compare the measured values and the calculated values obtained from the experiment. Compute the percentage error for all voltages and currents.
(b) As part of your laboratory report, use excel (x-y scatter plot) to plot the measured and calculated graphs for the data in tables 1, 2, and 3. Explain what these plots represent in your laboratory report. Your table must have gridlines and include a legend to distinguish between the measured and calculated data.
(c) In the discussion and conclusion section of your laboratory report, discuss any difficulties encountered in the lab, any possible sources or error and what you learned from this experiment.
Attachment:- images.pdf