Exercise Questions|Section 25.1 Current

25.1 . Lightning Strikes. During lightning strikes from a cloud to the ground, currents as high as 25,000 A can occur and last for about 40 micro sec. How much charge is transferred from the cloud to the earth during such a strike?

25.2 . A silver wire 2.6 mm in diameter transfers a charge of 420 C in 80 min. Silver contains free electrons per cubic meter.
(a) What is the current in the wire? (b) What is the magnitude of the drift velocity of the electrons in the wire?

25.3 . A 5.00-A current runs through a 12-gauge copper wire (diameter 2.05 mm) and through a light bulb. Copper has free electrons per cubic meter. (a) How many electrons pass through the light bulb each second? (b) What is the current density in the wire? (c) At what speed does a typical electron pass by any given point in the wire? (d) If you were to use wire of twice the diameter, which of the above answers would change? Would they increase or decrease?

25.6 . Consider the 18-gauge wire in Example 25.1. How many atoms are in of copper? With the density of free electrons given in the example, how many free electrons are there per copper atom?

25.7 .The current in a wire varies with time according to the relationship (a) How many coulombs of charge pass a cross section of the wire in the time interval between and (b) What constant current would transport the same charge in the same time interval?