Verifying Ohm’s law
Vary the current through a resistor, record current and voltage, and find its resistance from the V–I graph.
Objectives
- Connect an ammeter in series and a voltmeter in parallel.
- Show that current is proportional to potential difference.
- Find resistance from a graph.
Theory
Ohm’s law: the current through a metallic conductor is directly proportional to the potential difference across it, provided its temperature stays constant. V = IR, so a graph of V against I is a straight line through the origin whose gradient is the resistance R. The rheostat changes the total resistance of the circuit and therefore the current.
V = IR
Procedure
- Take a first pair of readings from the ammeter and voltmeter.
- Change the rheostat and take readings at five or more different settings.
- Plot voltage against current in the Graph tab and note the gradient.
Precautions
- Start with the rheostat at a high resistance.
- Keep the current below the ammeter’s 1 A range.
- Open the key between readings so the resistor does not heat up.
- Subject
- Physics
- Grade
- 10–11
- Chapter
- Current Electricity (Nepal National Curriculum (CDC), grade 10)
- Difficulty
- Easy
- Duration
- 20 min
- Safety level
- Low
- Version
- 1.0
Apparatus
- Cells
- Rheostat
- Resistor
- Digital ammeter (0–1 A)
- Digital voltmeter (0–10 V)
- Key
- Connecting wires
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