This experiment verifies Ohm’s Law by measuring the current through a resistor as the voltage across it is varied. By plotting a graph of voltage versus current, the resistance of the resistor can be determined.
What This Experiment Demonstrates
Linear relationship between voltage and current for a resistor
Determination of resistance from the slope of the V-I graph
Practical use of ammeters and voltmeters
Apparatus Required
DC power supply (adjustable voltage)
Resistors of known or unknown resistance
Ammeter (0–1 A range)
Voltmeter (0–10 V range)
Connecting wires with banana plugs or crocodile clips
Switch
Breadboard (optional)
Theory
Ohm’s Law states that the current through a conductor is directly proportional to the voltage across it, provided the temperature remains constant:
\[ V = IR \]
Where \(V\) is the voltage across the resistor, \(I\) is the current through it, and \(R\) is the resistance. By measuring \(V\) and \(I\) for different voltages, the resistance can be determined as the slope of the V-I graph.
Method
Set up the circuit: connect the resistor in series with the ammeter and switch; connect the voltmeter across the resistor.
Start with the power supply at zero voltage.
Close the switch and gradually increase the voltage in steps.
For each voltage, record the corresponding current from the ammeter.
Repeat for at least 5–6 different voltages covering the instrument’s range.
Plot a graph of voltage (V) on the y-axis and current (I) on the x-axis.
Determine the slope of the line, which gives the resistance \(R = V/I\).
Check that the line is straight to confirm Ohm’s Law.
Observations
Record voltage and current in a table:
Voltage across the resistor (V)
Current through the resistor (A)
Check for linearity in V-I values
Calculations
Plot voltage (V) against current (I).
Draw the best-fit line through the points.
The slope of the line gives the resistance: \(R = V/I\).
Compare the experimentally determined resistance with the nominal value if known.
Result
The graph of voltage against current is linear, confirming Ohm’s Law. The resistance of the resistor can be accurately determined from the slope of the V-I graph.
Notes & Tips
Ensure proper connection of ammeter in series and voltmeter in parallel.
Do not exceed the rated current or voltage of the instruments.
Take multiple readings for accuracy and consistency.
Use color-coded wires to avoid confusion in series/parallel connections.
Switch off the supply before changing the resistor.
Video Demonstration
Video courtesy of Make Me Scientific (YouTube). Used for educational purposes under YouTube’s embedding policy.