Practical Skills: Investigating Resistance

NexSolveAI O-Level Learning Hub™ · Original starter resource

Aim

Investigate current versus potential difference for a resistor at approximately constant temperature.

Apparatus & safety

Teacher-approved low-voltage DC supply, suitable resistor, ammeter, voltmeter, switch and leads. Never use mains electricity. Ask the teacher to select resistor ratings and safe limits; disconnect between readings to reduce heating.

Circuit figure

AVRLow-voltage supply · teacher checks circuit
Ammeter in series; voltmeter across the resistor.

Everyday life

A suitable resistor limits current in an LED circuit. This experiment helps explain how current changes with voltage; do not connect an LED directly to a battery without suitable current limiting.

Method

  1. Connect the ammeter in series and voltmeter in parallel across the resistor. Ask the teacher to check the circuit before switching on.
  2. Begin at a low voltage and take five readings within the teacher’s safe limits.
  3. Record voltage and current; repeat readings and note instrument resolution.
  4. Plot V on the vertical axis against I on the horizontal axis. Draw a best-fit line.
  5. Calculate resistance from the gradient ΔV/ΔI using widely spaced points on the line.
Potential difference / VCurrent / ARepeat / A
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Evaluate

Does your graph pass near the origin? How would heating affect the constant-temperature assumption? Distinguish instrument resolution from measurement uncertainty.