Resistors

Resistance and Resistivity

Resistance (R) is the measure of how much an object - a resistor - opposes the flow of electric current. The resistance of an object is measured in Ohms (<math>\Omega</math>)

Resistivity (<math>\Rho</math>) is a measure of how strongly a material opposes the flow of electric current. Resistivity is measured in ohm metres (<math>\Omega</math>m). Related wiki page: table of resistivities

The relationship between resistance and resistivity is:

<math>R = {l \cdot \rho \over A} \,</math>

where

"l" is the length of the object

"A" is the cross sectional area of the object (assuming constant), and

"ρ" is the resistivity of the material

Resistors

A resistor is a passive electrical device that has been manufactured specifically to add resistance to a circuit, to effect a voltage drop.

The mathematical equation that describes the relationship between resistanece, voltage drop and current through a resistor is known as Ohms Law

<math>I = \frac{V}{R}</math>

where

I is the current in amperes,

V is the potential difference between the ends of the resistor in volts, and

R is the resistance of the resistor, measured in ohms