### 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.