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Potential difference, emf, resistivity

Short answer

EMF is the energy supplied per unit charge by a source; potential diference is the energy used per unit charge between two points. EMF exists in source, PD across any element. Resistnce R=V/I (Ω) opposes current; resitivity ρ is a material's intrinsik property (Ω·m), R=ρl/A.

What is the difference between the potential difference and electromotive force? Define resistance and resistivity.

Difference between potential difference and EMF

PointEMFPotential difference
MeaningEnergy supplied by the source per unit chargeEnergy used between two points per unit charge
Exists inSource onlyAny two points / element
With no currentPresentZero across a resistor
ValueLarger (E = V + I r)Smaller than EMF for a loaded source
CauseChemical or magnetic actionCurrent through a resistance

Resistance

Resistance is the opposition offered by a material to the flow of current: R = V/I (ohm, Ω). For a conductor, R = ρ l/A, so it depends on length, area, material and temperature.

Resistivity

Resistivity (ρ) is the resistance of a unit cube of the material, measured between opposite faces: ρ = R A/l, in Ω·m. It depends only on the material and its temperature, not on its dimensions. Its reciprocal is conductivity σ = 1/ρ (S/m).

Example: copper has ρ ≈ 1.7 × 10⁻⁸ Ω·m; nichrome ≈ 1.1 × 10⁻⁶ Ω·m, so nichrome is used for heating elements.

✓ Answer checked by Claude Opus 5.5 (high effort)

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