Question

How long does it take electrons to get from a car battery to the starting motor? Assume the current is i and that the electrons travel through a copper wire with cross-sectional area Aand length L. The number of charge carriers per unit volume is n. State your answer in terms of the given variables, using e for the elementary charge.

Answer 1

Answer:

$t=\frac{L(nA)}{I}$

Explanation:

The concentration of electron/volume is n

A is the  cross-sectional Area

I the current

L the lenght

So,

The drift velocity of the electron is given by the equation,

$v = \frac{I}{n A}$ (1)

The time required is given by,

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

So putting (1) in (2) we have,

$t=\frac{L(nA)}{I}$