We have to calculate the time that electrons take to get from a car battery to the starting motor. We may assume that the current is 115 A and electrons travel through copper wire with cross-sectional area and length 85.5 cm.

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In copper on an average there is nearly one conduction electron per atom.

The density of copper, .

The molar mass of copper, .

Let the number of electrons per cubic meter in copper metal be n. Then, we have

,

where is the Avogadro number. We find

Let the drift speed of the electrons in the copper wire be . Then from the definition of current that it is the charge flow through the wire per second, we have

,

where A is the cross-sectional area of the wire and n is the number of conduction electrons per unit volume. Therefore, from the data of the problem we calculate the drift speed . It will be

Length of the copper wire from the connecting battery to the motor is 85.5 cm. Therefore, the time that electrons will take in reaching the motor from the car battery will be