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### Theory:

This experiment requires a coil of wire, a screw gauge, a metre scale, battery, key, ammeter, voltmeter, rheostat and connecting wires.

*An electric circuit*

**Formula**:

$R\phantom{\rule{0.147em}{0ex}}=\mathrm{\rho}\phantom{\rule{0.147em}{0ex}}\frac{L}{A}$

**Procedure**:

• Connect the battery, ammeter, wire, rheostat, and key in series, and the voltmeter in parallel to the unknown resistor.

• Close the key.

• Now, adjust the rheostat such that the ammeter reads a current of \(0.5\ A\).

• Note down the potential difference in the voltmeter.

• Again, adjust the rheostat and change the current in steps of \(0.5\ A\).

• For each current, note the corresponding potential difference in the voltmeter.

• Note down the values.

• Using a screw gauge and a metre scale, measure the diameter of the wire and the length of the coil, respectively.

**Observations**:

**(i) To find the resistance**:

S.No | Ammeter reading- \(I\) (Ampere) | Voltmeter reading- \(V\) (Volt) | Resistance\(=\) \(\frac {V}{I}\) (Ohm) |

1. | |||

2. | |||

3. | |||

4. | |||

5. | |||

6. |

**(ii) To find the diameter of the wire using screw gauge**:

S.No | Pitch scale reading(PSR) (\(mm\)) | Head scale coincidence (\(HSC\)) | Head scale reading\(HSR\) \(=\) \({HSC } \times {LC}\) (\(mm\)) | Total reading \(=\) \(PSR + HSR\) (\(mm\)) |

1. | ||||

2. | ||||

3. |

From the observed data, the resistivity of the material of the wire can be found using the formula.

To know more about screw gauge, click here.