| Lesson Plan |
| Grade: |
Date: 01/12/2025 |
| 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.
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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
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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.
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Lesson Structure:
- Do‑now (5') – short quiz on voltage‑divider calculations.
- Mini‑lecture (10') – derive the divider equation and introduce the concept of a null method using a galvanometer.
- Demonstration (15') – assemble the potential‑divider circuit, connect the galvanometer, and show the null point.
- Guided practice (15') – pairs adjust the variable resistor to achieve null, record settings, and solve for the unknown resistance.
- Error‑analysis discussion (10') – examine common error sources (zero drift, thermal EMF, contact resistance, supply fluctuation) and suggest mitigations.
- Exit ticket (5') – each student writes one sentence explaining why the null method reduces systematic error.
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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.
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