Electrical Resistance

Understanding electrical resistance and its properties.

What is Electrical Resistance?

Electrical resistance is a measure of the opposition to the flow of electric current in an electrical circuit. It is a fundamental property of materials that dictates how much current will flow for a given voltage. The SI unit of electrical resistance is the Ohm (Ω).

Factors Affecting Resistance

  • Material: Different materials have different inherent resistivities. Conductors (like copper) have low resistance, while insulators (like rubber) have very high resistance.
  • Length: The longer the conductor, the higher its resistance.
  • Cross-sectional Area: The larger the cross-sectional area of the conductor, the lower its resistance.
  • Temperature: For most conductors, resistance increases with increasing temperature.

Resistivity (ρ)

Resistivity is an intrinsic property of a material that quantifies how strongly it resists electric current. It is independent of the material's shape or size.

R = ρ × (L / A)
Where:
• R = Resistance (Ω)
• ρ = Resistivity (Ω·m)
• L = Length of the conductor (m)
• A = Cross-sectional area of the conductor (m²)

Common Resistivity Values

Material Resistivity (Ω·m at 20°C) Classification
Silver1.59 × 10-8Conductor
Copper1.68 × 10-8Conductor
Gold2.44 × 10-8Conductor
Aluminum2.82 × 10-8Conductor
Nichrome1.10 × 10-6Resistor Material
Silicon2.3 × 103Semiconductor
Glass1010 to 1014Insulator
Rubber1013 to 1016Insulator

Frequently Asked Questions

What is the difference between resistance and resistivity?

Resistance is a property of a specific object (like a wire) that depends on its material, length, and cross-sectional area. Resistivity is an intrinsic property of the material itself, independent of its shape or size.

How does resistance relate to Ohm's Law?

Ohm's Law (V = I × R) directly relates voltage (V), current (I), and resistance (R). Resistance is the proportionality constant between voltage and current.

See Also