Question

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 m3.

Answer 1

Answer:

t=13.49 min

Explanation:

Given that

I=300 A

A= 0.21 cm²

L= 0.85 m

Number of charge carriers per unit volume = 8.49 x 10²⁸ m⁻³.

We know speed of the electron given as

V=J/ne

J= I/A

So

V=I/neA

$V=\dfrac{300}{8.49\times 10^{28}\times 1.6\times 10^{-19}\times 0.21\times 10^{-4} }$

V=0.00105 m/s

lets take t is the time when electron travels from car battery to the starting motor

t = L/V

$t=\dfrac{0.85}{0.00105}$

t=809.52 s

t=13.49 min