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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 is the characteristic property of a material by which it resists the amount of current through it.

What is the SI Unit of resistivity?

SI Unit of resistivity is ohm meter.


We know that,

R = ρ (l/A)


ρ = R (A/l)

= ohm × m 2 /m

= ohm × m

Therefore, unit of rho is ohm meter.

Since, Resistance is directly proportional to length of the wire, if the length of the wire is doubled , resistance of the wire is also doubled. 

According to ohm's law,

Resistance is inversely proportional to current. So, if resistance is doubled then current is halved.

Therefore, the ammeter reading will be halved and the reading will be 50 mA.

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CA Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Economics, Accounting and English at Teachoo