How long does it take electrons to get from a car battery to the starting motor? Assume the current is 280 A and the electrons travel through a copper wire with cross-sectional area 0.44 cm2 and length 0.85 m. The number of charge carriers per unit volume is 8.49 ✕ 1028 m−3.

Explanation:

Given:

Current, i = 280 A

Cross-sectional area, A = 0.44 cm^2

Converting from cm^2 to m^2,

0.44 cm^2 × (1 m)^2/(100 cm)^2

= 0.44 × 10^-4 m^2

Length, L = 0.85 m

Number of charge carriers per unit volume, nv = 8.49 ✕ 10^28 m^−3

Current density, J = nv × q × v

I/A = nv × q × v

I = nv × A × q × (L/t)

t = (nv × A × q × L)/I

= (8.49 ✕ 10^28 × 0.44 × 10^-4 × 1.602 × 10^-19 × 0.85)/280

= 1816.7 s

Since 60 seconds = 1 minute

= 30.28 minutes

d) physical means can be used to separate the components of air.