Required practical 3

1. Set up a simple series circuit using a power supply, an ammeter, a switch, and a metre ruler with a thin resistance wire attached.

2. Connect a voltmeter in parallel across the section of test wire between two crocodile clips.

3. Attach the crocodile clips 10cm apart from each other.

4. Close the switch, quickly record the current and the potential difference immediately open the switch.

5. Move the crocodile clips 10cm apart until the measurements are up to 100 cm.

6. Calculate the resistance of each length using Volts=Current*Resistance.

Conclusion-The resistance of the wire is directly proportional to the length.

Key Sources of Error & Safety

• Heating Effect: Current flowing through the wire causes it to heat up, which increases resistance and corrupts results.

  • Fix: Use low potential difference

  • Fix: Switch off the circuit between readings to allow cooling

• Zero Error / Contact Resistance: Crocodile clips do not clip at exactly at 0cm, The clip and wire contact itself introduces extra resistance.

  • Fix: Subtract the offset constant reading if present.

Resistors in series and parallel

• Series Circuit: Adding resistors in series increases total resistance. The current must pass through each resistor in turn.

• Parallel Circuit: Adding resistors in parallel decreases total resistance . Providing additional pathways (branches) allows more total current to flow for the same potential difference.

Variables

• Independent Variable: Length of the wire.

• Dependent Variable: Resistance.

• Control Variables: Wire material, wire cross-sectional area (thickness), and temperature.