In 1828, George Simon Ohm, a German physicist, found that for many substances, the electrical current I flowing through them is proportional to the voltage V across their ends.

The empirical relationship 

                                    V I

is called Ohm's Law. The constant of proportionality, called the resistance and given the symbol R, is independent of V or I, but depends only on the substances and its shape and size. Thus Ohm's Law is

                                   V = R * I

Unit of Resistance:-

                         Volt per ampere OR Ohm ( W )

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