Resistance: Resistance & Resistivity

Resistance R = V/I V = voltage, I = current Scalar quantity Unit = ohm (Ω) Ohmeter - measures resistance

Resistance & energy loss As electric flows through a material, it heats it up The conversion from electrical potential to heat energy depends on the resistance High resistance means that a large percentage of the electrical energy is lost as heat

Ohm's Law Under constant physical conditions, the potential difference across a conductor is proportional to the current flowing through it V = IR

Combining Power, Joule's Law & Ohm's Law P = IV Joule's Law: W = I²Rt Ohm's Law: V = IR Energy output, W = VIt

Resistivity A constant associated with the resistance of a body Scalar quantity Unit = ohm metre (Ωm) Symbol = ρ

ρ = RA/l R = resistance A = cross-sectional area l = length

ρ = (Rπd²)/4l d = diameter π = mathematical constant, 3.14

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