State Ohm's law. Describe an activity to verify it, with a circuit diagram and the graph you expect.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · State the law in one line. At constant temperature, the current through a conductor is directly proportional to the potential difference across it: V ∝ I, so V = IR.
2 · Draw the circuit. [Circuit: battery, plug key, ammeter and nichrome wire XY in series; voltmeter across XY; + and − marked; current arrow]
3 · Describe the steps.
Start with one cell; close the key; note I and V.
Repeat with 2, 3 and 4 cells.
Find V/I for each reading.
4 · Draw the graph. [Graph: I (A) on the x-axis, V (V) on the y-axis, straight line through the origin]
5 · Write the result. V/I is the same each time and the V-I graph is a straight line through the origin, so Ohm's law is verified.
6 · Real life. Older fan regulators changed the resistance to change the current and the speed of the fan.
7 · Close in one line. Current rises in step with potential difference while the resistance stays fixed.
Scoring tip: Label both axes with units. Connect the voltmeter across the wire only, not across the battery.
