Ohm's Law

This demonstration uses a simple resistor circuit to verify the relationship ( V = IR ).

1. Gather equipment: a low-voltage DC power supply, a fixed resistor (e.g., 100 Ω), a voltmeter, an ammeter, and connecting leads.
2. Connect the resistor in series with the ammeter, and place the voltmeter across the resistor.
3. Switch on the power supply at a low voltage (e.g., 1 V). Record the current from the ammeter and the voltage from the voltmeter.
4. Increase the voltage step by step (e.g., in 1 V increments), recording the corresponding current at each step.
5. Plot a graph of voltage (y-axis) against current (x-axis). A straight line through the origin indicates ohmic behavior, with the slope equal to the resistance.
6. Repeat with different resistors to compare resistance values.

Ohm's Law I - TeachEngineering:

Ohm's Law with practical demonstration - Kitronik:

📄 Ohm's Law I - ncwit.org: https://www.teachengineering.org/activities/view/ohm1_act_joy

• Try with a variable resistor to show how changing resistance affects the current at a fixed voltage.

• Use a low-voltage DC power supply (typically under 12 V) to avoid electric shock.
• Do not exceed the power rating of the resistor to prevent overheating.
• Switch off the supply before changing connections.
• Allow bulbs or resistors to cool before handling if they become hot.

• What does the gradient of the voltage-current graph represent? (The resistance of the component.)
• Why does a straight-line graph through the origin indicate ohmic behavior? (Because voltage is directly proportional to current.)
• How does the graph for a filament bulb differ from a fixed resistor, and why? (It curves because resistance increases as the filament gets hotter.)
• What happens to current if voltage is doubled across an ohmic resistor? (Current also doubles, provided the resistance stays constant.)
• Why is it important to keep the temperature constant when testing Ohm’s law? (Because resistance can change with temperature, altering the relationship.)