Every body in relation to the electric current is characterized by its resistance.If you recall the electron theory, according to her, all substances are composed of atoms and molecules.These atoms and molecules in different materials have different structures.And they occur in the path of free electrons in a conductor when the electrical circuit is current.That is, when the free electron collides with the ion conductor material crystal lattice, it inevitably loses some of its kinetic energy and feels as if its resistance movement.

The greater resistance of the conductor, so it is worse than an electric current.Represented by the electrical resistance of the Latin letter R, and the unit of measurement adopted by the 1 ohm.

downside resistance characteristic of a substance is its conductivity.The higher the electrical conductivity of the material, the better it conducts current.Insulators are different from the conductivity of the conductors in a great number of times, measured in units of twenty two zeros!

## Resistivity.Determination and calculation

Thus, the electrical resistance depends on the material from which is made a conductor.But there are two important parameters - the length of the conductor and the cross-sectional area.Obviously, the longer the wire, the longer its substance ions will interfere with the movement of free electrons.

But to better understand why the resistance depends on the cross-sectional area, it is necessary to draw an analogy with water.Imagine two identical vessels connected in one case, the thin tube and the other - colon.On thin or thick tube water will spill from one vessel to another?It is clear that on the colon.
resistivity - the resistance conductor and a length of 1 meter and a cross section of 1 mm2.

smallest resistivity possess silver and copper.

Thus, to calculate the electrical resistance of the conductor, it is necessary to use the formula:
R = pl / S,
where p - resistivity, l - length of conductor, S - conductor cross-sectional area.

## Interesting facts

When the temperature of the metal conductor, the resistance increases.To explain this phenomenon is the fact that the heat transmission body increases the intensity of the motion of the atoms of its substance, and it is largely prevents the free flow of electrons.

lowered the temperature in metals are the best conditions for carrying an electric current.There is even such a thing as superconductivity, that is a state of a metallic conductor when its resistance is zero.The metal atoms almost freeze in place, absolutely without hindering the movement of free electrons.This happens at -273oS.