Assignment #4 Summer 2011 Assignment #4 - DC Circuits Chapter 27 27-3 . An aluminum wire having a cross-sectional area equal to 6 2 4 10 m-× carries a current of 5.00 A. The ( mass ) density of aluminum is 2.7 g/cm 3 . Assume each aluminum atom supplies one conduction electron per atom. Find the drift speed of the electrons in the wire. Atomic mass of aluminum (p. A-22 ) = 26.982 g / mole Avogadro’s number, N A 22 6.02 10 = × per mole 27-5 . Suppose the current in a conductor decreases exponentially with time according to the equation / ( ) , t o I t I e τ-= where I o is the initial current (at t = 0) and τ is a constant having dimensions of time. Consider a fixed observation point within the conductor. (a) How much charge passes this point between t = 0 and t = τ ? (b) How much charge passes this point between t = 0 and t = 10 τ ? (c) What if? How much charge passes this point between t = 0 and t = ∝ ? 27-17
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