# Factors Affecting Resistance of a Conductor

There is no ‘perfect’ electrical conductor; every conductor that makes up the wires has some level of resistance no matter what kind of material it is made from.

There are four main factors affecting the resistance in a conductor: The cross-sectional area of the wire (A), length of the conductor (ℓ), temperature (T), and resistivity of the material (ρ)

## Cross-sectional area of the wire (A)

More water will flow through a wider pipe than that through a narrow pipe. Similarly, the larger the diameter of the wire, the greater the cross-sectional area, the less the resistance in the wire, and the more the flow of current.

## Length (ℓ)

The longer the wire, the more the resistance and the more time is taken for the current to flow.

## Resistivity (ρ)

It is a measure for the opposition to flowing current through a material of the wire, or how difficult it is for current to flow through a material. The different materials have different resistivity, i.e. more or less resistance in the materials.

## Temperature (T)

The resistivity of a material is dependent upon the temperature surrounding the material. Resistivity increases with an increase in temperature for most materials. The table below lists the resistivity of some materials at 20 °C.

Factors affecting resistance can be mathematically expressed with the following formula:

A is the cross-sectional area, ℓ the length, T is the temperature, and ρ the resistivity (conducting ability of a material for a wire.)

**Example**

There is a copper wire 50 m in length with a cross-sectional area of 0.13 cm². What is the resistance of the wire?

The resistance of this copper wire is 0.0646 Ω. Although there is resistance in the copper wire, it is very small. A 50-m-long wire only has 0.0646 Ω resistance; thus we can say that copper is a good conducting material. Copper and aluminum are commonly used conducting materials with reasonable prices and better conductivity.