Potentiometer Advantage
Mediumphysics
Potentiometer preferred over voltmeter for measuring emf because?
Select the correct option:
Solution
Incorrect! Answer:
It draws no current from cell
- Voltmeter Limitation: A voltmeter requires some current to show a deflection. This current causes a voltage drop (Ir) across the internal resistance of the cell being measured. Thus, it measures terminal voltage (E−Ir), not true EMF (E).
- Potentiometer Mechanism: A potentiometer uses a 'null method'. At the balance point, the potential provided by the potentiometer wire exactly opposes the EMF of the cell.
- Result: At balance, zero current is drawn from the cell.
- Highest Precision: Because I=0, the measured potential difference is exactly equal to the EMF (E). It effectively acts like an infinite resistance voltmeter.
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About This Question
- Subject
- physics
- Chapter
- current electricity
- Topic
- potentiometer advantage
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
It draws no current from cell
- Voltmeter Limitation: A voltmeter requires some current to show a deflection. This current causes a voltage drop (Ir) across the internal resistance of the cell being measured. Thus, it measures terminal voltage (E−Ir), not true EMF (E).
- Potentiometer Mechanism: A potentiometer uses a 'null method'. At the balance point, the potential provided by the potentiometer wire exactly opposes the EMF of the cell.
- Result: At balance, zero current is drawn from the cell.
- Highest Precision: Because I=0, the measured potential difference is exactly equal to the EMF (E). It effectively acts like an infinite resistance voltmeter.
This medium difficulty physics question is from the chapter current electricity, covering the topic of potentiometer advantage. It appeared in the 2025 exam.
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