• 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 (ohms, Ω)

ρ = resistivity (ohm meter, Ω m)

l = length of conductor (m)

A = cross-sectional area of conductor (m²)

Resistivity of some Common Conductors

• Aluminum: 2.6 x 10^-8 Ω m
• Copper: 1.7 x 10^-8 Ω m

Resistivity of some Common Insulators

• bakelite: 1 x 10¹² Ω m
• glass: 1 x 10¹⁰ Ω m
• marble: 1 x 10⁸ Ω m
• mica: 1 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

Example - Resistance

The resistance of a 10 meter copper wire with a cross sectional area of 0.8 mm² can be calculated as

R = (1.7 x 10^-8 Ω m) (10 m) / ((0.8 mm²)(10^-6 m²/mm²))

    = 0.21 Ω

Create Date : 19 กุมภาพันธ์ 2557
Last Update : 19 กุมภาพันธ์ 2557 5:09:50 น.		5 comments
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