# HW1answers-1 - P 1.5 The charge on an electron is 1.6e-19...

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P 1.5 The charge on an electron is –1.6e-19 coulombs. A current of 1 ampere flows in a wire carried by electrons. How many electrons pass through a cross section of the wire each second? Hint- the definition of 1 amp of current is 1 coulomb of charge passing a point on the wire in 1 second. Answer: 1 amp = 1 C/s = N electrons/s x 1.6e-19 coulombs/electron N = 6.25e18 electrons per second P 1.6 The ends of a length of wire are labeled a and b . If the current in the wire is i ab = –5A, are the electrons moving toward a or b ? How much charge Q (not the # of electrons) passes through a cross section of the wire in 3 seconds? Answer: i ab means the current is from a to b but the –5A means the current is from b to a , but electrons flow in reverse, so the current is reversed again so that the electron flow is from a to b . The electrons are flowing toward b . For a constant current (DC), the charge Q flowing past a point in 3 seconds is Q = 5 amps x 3 seconds = 15 coulombs. P 1.13

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## This note was uploaded on 09/01/2010 for the course EE 331 taught by Professor Preston during the Spring '06 term at University of Texas at Austin.

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HW1answers-1 - P 1.5 The charge on an electron is 1.6e-19...

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