State the Ohm.s law. Explain how it is used to define the SI unit of resistance.

Explanation

If I is the current flowing through a conductor and V is the potential difference (or voltage) across its ends, then according to Ohm.s law,
I `prop` V (at constant temperature).
This can also be written as,
`V prop I`
`:.` V = (constant) I
`{:( :. V/I = "constant" ),( " "= R),( :. V = IR):}}` ... ...(12.4)
In equation (12.4), R is constant for the given metallic wire at a given temperature and is called its resistance.
Resistance is the property of a conductor to oppose the flow of charges through it.
The SI unit of resistance is ohm. It is represented by the Greek letter `Omega` (Omega).
According to Ohm.s law,
`R = V/t` ...... (12.5)
Definition of the SI unit of resistance : If the potential difference across the two ends of a conductor is IV and the current through it is 1 A, then the resistance R of the conductor is `1 Omega`.
`i.e., 1" ohm" = (1 "volt")/(1 " ampere") (1 Omega = 1V//1A)`