<Li> l is the length of the conductor, in m </Li> <P> Electricity is most commonly conducted in a copper wire . Copper has a density of 7000894000000000000 ♠ 8.94 g / cm, and an atomic weight of 6998635460000000000 ♠ 63.546 g / mol, so there are 7005140685500000000 ♠ 140 685. 5 mol / m . In one mole of any element there are 7023602000000000000 ♠ 6.02 × 10 atoms (Avogadro's constant). Therefore in 7000100000000000000 ♠ 1 m of copper there are about 7028850000000000000 ♠ 8.5 × 10 atoms (7023602000000000000 ♠ 6.02 × 10 × 7005140685500000000 ♠ 140 685. 5 mol / m). Copper has one free electron per atom, so n is equal to 7028850000000000000 ♠ 8.5 × 10 electrons per cubic metre . </P> <P> Assume a current I = 1 ampere, and a wire of 6997200000000000000 ♠ 2 mm diameter (radius = 6997100000000000000 ♠ 0.001 m). This wire has a cross sectional area of 6994314000000000000 ♠ 3.14 × 10 m (A = π × (6997100000000000000 ♠ 0.001 m)). The charge of one electron is q = 3018840000000000000 ♠ − 1.6 × 10 C. The drift velocity therefore can be calculated: </P> <Dl> <Dd> u = I n A q u = 1 C / s (8.5 × 10 28 m − 3) (3.14 × 10 − 6 m 2) (1.6 × 10 − 19 C) u = 2.3 × 10 − 5 m / s (\ displaystyle (\ begin (aligned) u& = (I \ over nAq) \ \ u& = (\ frac (1 (\ text (C)) / (\ text (s))) (\ left (8.5 \ times 10 ^ (28) (\ text (m)) ^ (- 3) \ right) \ left (3.14 \ times 10 ^ (- 6) (\ text (m)) ^ (2) \ right) \ left (1.6 \ times 10 ^ (- 19) (\ text (C)) \ right))) \ \ u& = 2.3 \ times 10 ^ (- 5) (\ text (m)) / (\ text (s)) \ end (aligned))) </Dd> </Dl>

Relation between drift velocity and length of conductor