What is electrical resistivity ? In a series electrical circuit comprising a resistor made up of a matallic wire, the ammeter reads `5 A`. The reading of the ammeter decreases to half when the length of the wire is doubled. Why ?

Explanation

The electrical resistance of a conductor made of that material of unit length and unit cross-setional area.
The resistance of an uniform conductor is given by
`" "R = p(l)/(A)`
where, I is the length of the conductor
p is the electrical resistivity of the material
A is the cross-sectional area.
If I is doubled, then R is also doubled.
So, in this case, `R^(') = p(2l)/(A) = 2(pl)/(A) = 2R`
Since, `I = (V)/(R)`
So, `I' = (V)/(2R) = (I)/(2)`
when, R is doubled, I becomes `(I)/(2)`.