Question

How long does it take electrons to get from the car battery to the starting motor? Assume the current is 143 A and the electrons travel through copper wire with cross sectional area 40.2 mm2 and length 84.5 cm . The mass density of copper is 8960 kg/m3 and the molar mass is 63.5 g/mol . Avogadro’s number is 6.022 × 1023 . Assume that each copper atom contributes one conduction electron.

Answer 1

Answer

the concentration of electron/ volume (n) = 8.5 × 10²⁸ /m³

the drift velocity of electron

$v = \dfrac{I}{neA}$

$v = \dfrac{143}{8.5\times 10^{28}\times 1.6\times 10^{-19}\times 40.2 \times 10^{-6}}$

v = 2.615 × 10⁻⁴ m/s

time require is

$t=\dfrac{L}{v}$

$t=\dfrac{0.845}{2.615\times 10^{-4}}$

t = 3231.35 s