What is electrical resistivity? Derive its SI unit. In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads 100 mA. If the length of the wire is doubled, how will the current in the circuit change? Justify your answer.


Electrical resistivity of the material of a conductor is the resistance offered by the conductor of length 1 m and area of cross-section 1 m2.

ρ = RA/l

unit of ρ = ohm metre2 / metre = ohm metre

Resistance of wire is doubled if its length is doubled.

Hence current is reduced to half.

∴ Ammeter reading = 100 mA / 2

= 50 mA

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