Translate

Electrical resistance of an electrical conductor depends on

  • The length of the conductor
  • The material of the conductor
  • The temperature of the material
  • The cross-sectional area of the conductor

and can be expressed as

R = ρ L / A               (1)

where

R = resistance of the conductor (ohms, Ω)

ρ = resistivity of the conductor material (ohm metre, Ω m)

L = length of conductor (m)

A = cross-sectional area of conductor (m2)

Resistivity of some Common Conductors

Aluminum: 2.65 x 10-8 Ω m (0.0265 μΩ m)

Carbon: 10 x 10-8 Ω m (0.10 μΩ m)

Copper: 1.724 x 10-8 Ω m (0.0174 μΩ m)

Iron: 10 x 10-8  Ω m (0.1 μΩ m)

Silver: 1.6 x 10-8 Ω m (0.0265 μΩ m)

Note that resistivity depends on temperature. The values above are for temperatures 20 oC.

Resistivity, Conductivity and Temperature Coefficients for some Common Materials

Resistivity of some Common Insulators

bakelite: 1 x 1012 Ω m

glass: 1 x 1010 - 1 x 1011 Ω m

marble: 1 x 108 Ω m

mica: 0.9 x 1013 Ω m

paraffin oil: 1 x 1016 Ω m

paraffin wax (pure): 1 x 1016 Ω m

plexiglass: 1 x 1013 Ω m

polystyrene: 1 x 1014 Ω m

porcelain: 1 x 1012 Ω m

pressed amber: 1 x 1016 Ω m

vulcanite: 1 x 1014 Ω m

water, distilled: 1 x 1010 Ω m

Note that good conductors of electricity have low resistivity and good insulators have high resistivity.

Example - Resistance of a Conductor

The resistance of 10 meter gauge 17 copper wire with cross sectional area 1.04 mm2 can be calculated as

R = (1.7 x 10-8 Ω m) (10 m) / ((1.04 mm2)(10-6 m2/mm2))

    = 0.16 Ω

Example - Cross-sectional area and Resistance

The copper wire above is reduced to gauge 24 and cross-sectional area 0.205 mm2. The increase in resistance can be calculated to

R = (1.7 x 10-8 Ω m) (10 m) / ((0.205 mm2)(10-6 m2/mm2))

    = 0.83 Ω

Thanks for reading - Electrical resistance and resistivity
Naitik Patel
Industrial Guide

Share this blog with your friends from here 👇

Previous Post Next Post