Wednesday, November 5, 2008

Resistance: Ohm's Law

Resistance is the opposition put up by matter to the passage of a steady electric current through it. We can say that conductive materials such as aluminum offer the least resistance to the flow of electrons (electrical current), whereas the insulating materials, such as plastic and wood, offer strong resistance. In physics the electrical unit of resistance is called Ohm (Ω).

The resistance of a wire is directly proportional to its length, and inversely proportional to its width. That is to say that the longer the wire is, the more resistance it will offer; and the wider it is, the less resistance it will offer. So, Ω=length/width.

Ohm's law: the Ohm's law states that the strength of an electric current through a conductor between two points is directly proportional to the potential difference (the voltage) across the two points, and inversely proportional to the resistance between them. The equation that describes this relationship is:
I= V/Ω, whereas I is the current in ampere, V the potential difference in volts, and Ω the resistance. The law was named after the German physicist Georg Ohm, who described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire.