Questions from potentiometer

 Potentiometer

Questions from potentiometer

Q1. Why is a potentiometer preferred over a voltmeter for measuring the emf of a cell?

Ans. Potentiometer work on null method, It does not draw any current from the cell thus there there is no potential drop due to the internal resistance of the cell. It measures the potential difference in an open circuit which is equal to the actual EMF of the cell. It is very accurate device.
On the other hand, voltmeter draw small current from the cell for its operation. So it measures terminal potential difference in a closed circuit which is less than EMF of the cell

Q2. The sensitivity of a potentiometer increases with increase in length of its wire. Explain why?

Ans. When the length of the wire increases the fall of potential per unit length of the wire become smaller (i.e potential gradient K= V/L ). Hence even a small potential difference can be measured.

Q3. Sometime the balance point in the potentiometer may not be obtained on the wire explain why?

Ans. When the EMF of the driving cell ,(auxiliary cell ) is less than the EMF of the cell being measured. We do not get balance point any where on the wire of potentiometer.

Q4. In a potentiometer experiment why it is is necessary to use a long wire?

Ans. Longer wire has a small potential gradient K= V/L ) consequently it is more sensitive and hence preferred.