The electrical resistance of the material depends on its length, area, and resistivity by the following relationship.

Technically the rate of change of resistance is measured in terms of the temperature coefficient of the material. Greek symbol Î± represents temperature coefficient of the material.

Resistance = [Resistivity * Length] / Area

Where

- Resistivity = â„¦-m
- Area = m
^{2} - Length = m

The resistivity (â„¦-m) is the temperature dependent physical property of the material. A change in temperature impacts the resistivity of material which in turn alters the resistance.

Technically the rate of change of resistance is measured in terms of the temperature coefficient of the material. Greek symbol Î± represents temperature coefficient of the material.

The equation below is used to find the resistance of object at any temperature when the resistance at some specific temperature is known.

R

R

Î±

T

T

The temperature coefficient of commonly used materials at 0, 20° C is given below:

**R**

_{2}= R_{1 }[ 1 + Î±_{1 }(T_{2 }- T_{1})]*where*R

_{1 }= Conductors resistance at temperature T_{1}R

_{2 }= Conductors resistance at temperature T_{2}Î±

_{1}= Temperature coefficient of the materialT

_{1 }= Reference temperature at which Î±_{1}is specifiedT

_{2 }= Conductor present temperatureThe temperature coefficient of commonly used materials at 0, 20° C is given below:

Materials | at 20 degree C | at 0 degree C |
---|---|---|

Aluminum | 0.00391 | 0.00424 |

Copper | 0.00393 | 0.00427 |

Iron | 0.0055 | 0.00618 |

Silver | 0.0038 | 0.00412 |

*Example: Copper wire has the resistance of 15 ohms at 20° C. Calculate the resistance at 80° C*
Solution: R

_{2}= R_{1 }[ 1 + Î±_{1 }(T_{2 }- T_{1})]
R

_{2}= 15 â„¦ [ 1 + 0.00393_{ }(80_{ }- 20)]
R

_{2}= 15 â„¦ ( 1.2358 )**R**

_{2}= 18.53 â„¦

**Positive temperature coefficient vs Negative temperautre coefficient**

The material whose temperature increases with increase in temperature is known as positive temperature coefficient. While material whose temperature decreases with increases in temperature is known as positive temperature coefficient.

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