Electrical Resistance
A measure of the opposition that a circuit element or material presents to the flow of electric current.
Governing formula
R = V / I = ρ L / A
SI unit
Ω (Ohms = V/A)
In depth
Resistance converts electrical energy into thermal energy through inelastic collisions between drift electrons and the vibrating crystal lattice ions (Joule heating). Resistance increases with conductor length L and material resistivity ρ, and decreases with larger cross-sectional area A.
Examples in the real world
Nichrome heating elements in a toaster offering ~20 Ω of resistance to glow red-hot, or precision carbon-film resistors on printed circuit boards.