## 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.

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Answer:
**

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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.

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Explanation.
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We know that,

R = ρ (l/A)

Therefore,

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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