Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: recall and use the principle of the potentiometer as a means of comparing potential differences
Learning Objective/s:
  • Recall the principle of a potentiometer and its relation to a uniform potential gradient.
  • Explain how a potentiometer can be used to compare unknown emf values by a null measurement.
  • Derive the relationship between balance length and emf and apply it to calculate voltages.
  • Identify common sources of error in potentiometer measurements and suggest ways to minimise them.
Materials Needed:
  • Potentiometer wire assembly with sliding contact
  • Stable adjustable DC driver (reference voltage source)
  • Galvanometer or sensitive voltmeter
  • Two unknown emf cells (batteries)
  • Ruler or calibrated scale for measuring balance length
  • Connecting leads and crocodile clips
  • Whiteboard or projector for diagrams
 Introduction:
Begin with a quick demonstration of a sliding contact moving along a uniform wire, asking students what they notice about the voltage drop. Review the concept of a potential divider and the idea of a linear potential gradient from previous lessons. Explain that today they will use a potentiometer to compare unknown voltages without drawing current, and success will be measured by correctly determining emf values from balance lengths.
Lesson Structure:
  1. Do‑now (5'): Students answer a short question on potential dividers displayed on the board.
  2. Mini‑lecture (10'): Derive \(V(x)=\frac{V_{\text{total}}}{L}x\) and relate it to a series of resistors.
  3. Demonstration (10'): Set up the potentiometer circuit, adjust the driver, and show the null condition with a known voltage.
  4. Guided practice (15'): In pairs, students measure balance lengths for two unknown emf cells, record \(l_1\) and \(l_2\), and calculate the emf values using the proportionality.
  5. Concept check (5'): Whole‑class discussion of results, highlighting common pitfalls.
  6. Extension activity (5'): Solve a practice problem on potential‑divider output voltage.
Conclusion:
Summarise that the potentiometer provides a high‑precision, zero‑current method for comparing voltages and that the emf is directly proportional to the balance length. Ask students to write one key advantage of the potentiometer on an exit ticket. For homework, assign the practice questions from the source worksheet.