**To Study The Variation in Potential Drop With Length of a Wire For a Steady Current**

**Aim**

To study the variation in potential drop with length of a wire for a steady current.

**Apparatus and material**

**Apparatus. Potentiometer:**

**Material:** A fully charged 4.5 V battery or battery eliminator, a low resistance rheostat, a voltmeter of range (0-3.0 V), an ammeter (0-3) A, a one way key, a jockey, a set square, connecting wires and a piece of sand paper.

**Theory**

For a potentiometer with wire of uniform material density and thickness (cross-sectional area) carrying a steady current, potential drop is proportional to the length of the wire.

where K is the drop of potential per unit length. It is called the potential gradient.

**Diagram**

**Procedure**

- Draw a circuit diagram showing the scheme of connections as in figure.
- Remove the insulation from the ends of the connecting copper wires with a sand paper.
- Connect the positive pole of the battery (eliminator) (a battery of constant e.m.f.) to the zero end (P) of the potentiometer and the negative pole through a one-way key, an ammeter and a low resistance rheostat to the other end (Q) of the potentiometer.
- Connect the positive terminal of the voltmeter to the end P of the potentiometer and the negative terminal to the jockey.
- Touch the end of the jockey to the end Q of the potentiometer.
- Close the key and set the rheostat such that the voltmeter gives full scale deflection (3 V).
- Touch the jockey at end P at 0 (zero) cm. The voltmeter will give zero deflection.
- Touch the jockey at marks separated by 50 cm length of wire. Note the voltmeter reading in each case.
- Record your observations in tabular form as given ahead.

**Observations and Calculations**

**Calculation from graph**

Plot a graph choosing a suitable scale, for the values of potential drop V along y-axis and length l along x-axis as shown in figure.

**Result**

## Comments by Paras