Ohm’s law

A/L Physics · G.C.E. Advanced Level · Grades 12–13

Aim

To verify Ohm’s law and find the resistance of a resistor.

Apparatus

• A resistor of unknown value
• Ammeter and voltmeter
• Variable DC supply and wires

Method

1. Connect the resistor in series with the ammeter and the voltmeter across it.
2. Set the voltage V.
3. Read the current I.
4. Repeat for 6 values of V.
5. Plot V against I; the gradient = R.

Conclusion

V ∝ I (a straight line through the origin), so the resistance R = V ÷ I is constant: it is the gradient of the graph.