1.

Derive a formula that shows the relation between resistance length and area of cross section of a conductor.

Answer»

Solution :1. Resistance of a CONDUCTOR `(R)` is directly proportional to its length (l) for a constant potential DIFFERENCE.
`Ralphal""-(1)`
2. Resistance of a conductor is inversely proportional to its cross section area.
`Ralpha(1)/(A)""-(1)`
3. From (1) and (2), we get `Ralpha(1)/(A)` (at constant temperature)
`rArrR=(rho1)/(A)`
Where, `rho` is a proportionalty constant and it is CALLED SPECIFIC RESITANCE or resistivity.
4. The S.I. unit of resistivity is `Omega-m.`


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