Resistance is the opposition a material offers to the flow of current.
- Symbol: R
- Unit: ohm (Ω)
Resistance of a wire: R = ρL / A, where ρ is the material's resistivity, L is length and A is cross-sectional area. Longer or thinner wires have higher resistance.
Conductors (copper, aluminium, silver) have very low resistance. Insulators (rubber, plastic, glass) have very high resistance. Semiconductors (silicon, germanium) are in between and are the basis of modern electronics.