State the working principle of potentiometer. With the help of the circuit diagram, explain how a potentiometer is used to compare the emf's of two primay cells. Obtain the required expression used for comparing the emfs. Write two possible causes for one sided deflection in a potentiometer experiment.

Explanation

### Step-by-Step Solution

**1. State the Working Principle of a Potentiometer:**
The working principle of a potentiometer is based on the fact that the potential drop across a segment of a wire of uniform cross-section is directly proportional to its length. This means that if we have a wire of uniform material and cross-section, the voltage drop across any length of that wire can be calculated using the formula:
\[ V = k \cdot L \]
where \( V \) is the potential drop, \( k \) is a constant (related to the resistivity of the wire), and \( L \) is the length of the wire.

**2. Circuit Diagram Explanation:**
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