VIVA QUESTIONS WITH ANSWERS
Experiment No - 04: To compare the EMFs of given two cells using a potentiometer
01. Why is a potentiometer is preferred to measure or compare EMFs of cells instead of using a voltmeter?
Answer: Potentiometer has two advantages:
01. It draws no current from the voltage source being measured.
02. EMF measured by potentiometer is unaffected by the internal resistance of the source.
02. What do you mean by the EMF of a cell?
Answer: EMF is the potential difference between the positive and negative terminals of the cell when the circuit is said to be open.
03. What is the difference between using a potentiometer having a wire of length 1m and another having a wire length of 100m or 10m?
Answer: Accuracy in balancing length readings will be more if we use longer wires (say 100m length)
04. What is a potential gradient?
Answer: Potential drop per unit length of the wire is called the potential gradient.
05. Is it necessary that the area of the cross-section of the wire be uniform?
Answer: Yes. If the area of the cross-section is uniform, then the resistance per unit length of the wire is uniform and hence potential gradient is uniform.
06. What is a potentiometer?
Answer: It is an instrument used to measure potential difference or EMF of the cell.
07. Why is it called as a potentiometer?
Answer: Because it measures potential difference between any two points of electric circuits.
08. What is the principle of potentiometer?
Answer: It works on the principle that for a constant current ,fall of potential along uniform resistance wire is directly proportional to its length.
09. What do you mean by sensitivity of a potentiometer?
Answer: Sensitivity of a potentiometer is a smallest potential difference that it can measure.
10. How does the potential gradient very along the length of the potentiometer wire?
Answer: A sensitive galvanometer will respond to even a small departure from the exact balance point and will hence enable us to locate the balence point with the greater precision.
11. Why is a potentiometer preferred over a voltmeter for measuring the EMF of the cell?
Answer: A potentiometer draws no current from the cell whose EMFs is to be measured. On the other hand , the voltmeter always draws some current.
12. On what factors does the potential gradient depend?
Answer: Potential gradient depends directly on the strength of the current and resistance per unit length of a wire.
13. Under what conditions deflection in the galvanometer is shaky?
Answer: The reason as follows below:
01. The EMF of the battery of the cells may be fluctuating.
02. The circuit has a loose contact somewhere.
14. How does the potential gradient vary along the length of the potentiometer wire?
Answer: Potential gradient is same throughout the potentiometer wire.
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