Ohm's Law

When a steady current is made to flow through a metallic conductor, by maintaining a steady potential difference V across it, the current produced I, is experimentally found to be proportional to the potential difference. Thus it is found the the ratio V / I remains constant.
This V / I is called the resistance, R, of the metallic conductor.

R=	V

	I

This is called Ohm's Law. The situation is shown in a graph to the left. Note that the graph is a straight line, passing through the origin, and the graph is symmetrical about the origin. In other words: if the terminals of the battery applied across the conductor are reversed, one gets the same magnitude of current, but in the opposite sense.

Units of resistance:

From the definition:

R=	[V]	=	V

	[I]		A

[The unit of resistance is equal to the unit of voltage divided by current, which are the V (Volt) and A (Ampere)].

In honor of Georg Simon Ohm (1789 - 1854), the unit of resistance is called the Ohm ($\Omega$).

1 $\Omega$=	1 V

	1 A

It is important to note that Ohm's Law is not always valid, but it is a good empirical rule for most systems. One does come across situations in which the current is not proportional to the applied potential difference, for example in a semiconductor diode, or in the electrolysis of many electrolytes. Fortunately, these topics lead a little too far from the purpose of this course. So will limit ourselves to the cases where Ohm's Law is valid.