19_InstSolManual_PDF_Part1

# 19_InstSolManual_PDF_Part1 - CURRENT, RESISTANCE, AND...

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Unformatted text preview: CURRENT, RESISTANCE, AND DIRECT-CURRENT CIRCUITS 19 13. C 14. A 15. E Answers to Multiple-Choice Problems 1. B 2. B 3. D 4. B, D 5. A 6. A 7. C 8. A 9. C 10. C 11. C 12. C Solutions to Problems 19.1. Set Up: 1A 5 1 C / s. An electron has charge of magnitude e 5 1.60 3 10219 C. The current tells us how much charge ﬂows in a given time. We can ﬁnd the number of electrons that correspond to a certain amount of charge. 1 5 9.38 3 1018 electrons / s Solve: (a) 1.50 A 5 1 1.50 C / s 2 219 1.60 3 10 C / electron (b) D Q 5 ID t 5 1 1.50 A 2 1 300 s 2 5 450 C DQ 7.50 C 5 5 5.00 s (c) D t 5 I 1.50 A Reﬂect: The amount of charge associated with typical currents is quite large. In Chapter 17 we found that the force between objects that have net charge 1.0 C is immense. The same amount of charge enters and leaves any part of the circuit each second and each circuit element remains neutral. DQ Dt Solve: D Q 5 ID t 5 1 25,000 A 2 1 40 3 1026 s 2 5 1.0 C 1 2 19.2. Set Up: I 5 19.3. Set Up: The number of ions that enter gives the charge that enters the axon in the speciﬁed time. I 5 Solve: D Q 5 1 5.6 3 1011 ions 2 1 1.60 3 10219 C / ion 2 5 9.0 3 1028 C I5 DQ 9.0 3 1028 C 5 5 9.0 m A Dt 10 3 1023 s DQ . Dt 19.4. Set Up: Negative charge moving from A to B is equivalent to an equal magnitude of positive charge going from DQ . The current direction is the direction of ﬂow of positive charge. Dt Solve: The total positive charge moving from B to A is D Q 5 1 5.11 3 1018 1 2 3 3.24 3 1018 4 2 1 1.60 3 10219 C 2 5 DQ 1.85 C 1.85 C. I 5 5 5 62 mA. Positive charge ﬂows from B to A so the current is in this direction. Dt 30 s B to A. I 5 19.5. Set Up: D Q 5 ID t gives the amount of charge that passes a point in the wire in time D t. From D Q we can ﬁnd the number of electrons, since an electron has charge 2e. 1 5 3.44 3 1016 electrons / s Solve: 1 5.50 3 1023 C / s 2 1.60 3 10219 C / electron Reﬂect: Typical currents correspond to the ﬂow of a large number of electrons. 1 2 19-1 ...
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## This note was uploaded on 03/06/2009 for the course PHYS 114 taught by Professor Shoberg during the Spring '07 term at Pittsburg State Uiversity.

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