26_Chapter 18 HomeworkCH18 Direct-Current Circuits

26_Chapter 18 HomeworkCH18 Direct-Current Circuits - 124...

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124 CHAPTER 18 18.41 (a) The area of each surface of this axon membrane is () ( ) ( ) 66 2 0.10 m 2 10 10 m 2 10 m Ar ππ π −−  == × = ×  A 2 and the capacitance is 62 12 2 2 0 -8 21 0 m 3.0 8.85 10 C N m 1.0 10 m A C d κ  × =∈ = ×  ×  8 1.67 10 F = × In the resting state, the charge on the outer surface of the membrane is ( ) 83 9 1.67 10 F 70 10 V 1.17 10 C 1.2 10 i i QCV =∆ = × × = × → × 9 C The number of potassium ions required to produce this charge is 9 9+ -19 K 1.17 10 C 7.3 10 K ions 1.6 10 C i Q N e + × = × × and the charge per unit area on this surface is 92 -6 2 -19 1.17 10 C 1 10 m 0 m1 . 6 1 0 C 1 Å i Q A σ × ×× 0 2 2 24 2 1 1 8.6 10 Å 290 Å ee = = × 2 e This corresponds to a low charge density of one electronic charge per square of side 290 Å, compared to a normal atomic spacing of one atom per several Å . (b) In the resting state, the net charge on the inner surface of the membrane is
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This document was uploaded on 10/20/2011.

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