How long does it take electrons to get from a car battery to the starting motor? Assume the current is 300 A and the electrons travel through a copper wire with cross-sectional area 0.21 cm2 and length 0.85 m. The number of charge carriers per unit volume is 8.49 $ 1028 m#

808.25 seconds

Explanation:

From the relation,

If t = time

v = velocity

l = length

The current density, J, of a charge is given by:

Where number of charge carriers per unit volume n = 8.49 * 10²⁸

Charge of the electron, q = 1.6 * 10⁻¹⁹

Cross sectional area of the wire, A = 0.21 cm² = 0.000021 m²

Equating (1) and (2)

Since t = l/v.......(3)

Put the formula for v into equation (3)

t = 808.25 seconds

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wavelength divides in half and speed stays the same.