386. Problem 32.13 (RHK) 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
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Solution: Click For PDF Version 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
Let the drift speed of the electrons in the copper wire be
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
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 |