What is electrical resistivity of a material? What is its unit? Describe an experiment to study the factors on which the resistance of conducting wire depends.

Electrical resistivity of a material is the resistance of the conductor made of a material for unit length and unit cross section. It is represented with letter ρ

$P=\frac{RA}{l}$

Set an electric circuit consisting of a cell, an ammeter, a nichrome wire of length l and a plug key, as shown in the figure below.

1. Now, plug the key. Note the current in the ammeter.

2. Replace the nichrome wire by another nichrome wire of same thickness but twice the length, i.e., 2l

3. Now replace the wire by a thicker nichrome wire, of the same length l. A thicker wire has a larger cross-sectional area. Again, note down the current through the circuit.

4. Instead of taking a nichrome wire, connect a copper wire in the circuit. Let the wire be of the same length and same area of cross-section as that of the first nichrome wire. Note the value of the current. Notice the difference in the current in all cases.

You can notice resistance gets doubled once length is doubled and halved when area is doubled

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