Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: understand the use of a galvanometer in null methods
Learning Objective/s:
  • Describe the principle of a potential divider and write its governing equation.
  • Explain how a galvanometer detects the null condition in a Wheatstone‑type circuit.
  • Apply the null‑method relation to calculate an unknown resistance.
  • Identify common sources of error in null‑method measurements and propose mitigation strategies.
Materials Needed:
  • Regulated DC power supply (≈12 V)
  • Fixed resistors (e.g., 2 kΩ, 1 kΩ)
  • Variable/adjustable resistor
  • Sensitive galvanometer or digital null detector
  • Breadboard and connecting wires
  • Multimeter for verification
  • Worksheet with calculation tasks
 Introduction:
Begin with a quick question on how voltage dividers are used in everyday devices to spark curiosity. Recall the formula \(V_{R_2}=V_s\frac{R_2}{R_1+R_2}\) and link it to the need for precise measurements. State that by the end of the lesson students will be able to set up a null‑method experiment and interpret the results.
Lesson Structure:
  1. Do‑now (5') – short quiz on voltage‑divider calculations.
  2. Mini‑lecture (10') – derive the divider equation and introduce the concept of a null method using a galvanometer.
  3. Demonstration (15') – assemble the potential‑divider circuit, connect the galvanometer, and show the null point.
  4. Guided practice (15') – pairs adjust the variable resistor to achieve null, record settings, and solve for the unknown resistance.
  5. Error‑analysis discussion (10') – examine common error sources (zero drift, thermal EMF, contact resistance, supply fluctuation) and suggest mitigations.
  6. Exit ticket (5') – each student writes one sentence explaining why the null method reduces systematic error.
Conclusion:
Recap the steps of setting up a null‑method measurement and the key advantages of using a galvanometer. Ask a few students to share their calculated resistance values and how they checked for errors. Assign a homework problem: design a null‑method circuit to determine an unknown capacitor’s value using a bridge arrangement.