Chapter20

# Chapter20 - 634 CHAPTER 20 Section 20.9 ELECTRIC CIRCUITS...

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(el (b) 4LO (a) Section 20.13 RC Circuits 20. The time constant of an RC circuit is 2.6 s. How much time tis required for the capacitor (uncharged initially) to gain one-half of its full equilibrium charge? minus signs. However, one resistor is marked incorrectly. Which 0 is it? (a) R I (b) R 2 (c) R 3 (d) R 4 Section 20.12 Capacitors in Series and in Parallel 18. Three capacitors are identical, each having a capacitance C. Two of them are connected in series. Then, this series combinatiol is connected in parallel with the third capacitor. What is the equiva· lent capacitance of the entire connection? (a)! C (b) ~ C (c) 3 (dHC (e)§C T This icon represents a biomedical application. 11. Two wires are identical, except that one is aluminum and one is copper. The aluminum wire has a resistance of 0.20 fl. What is the resistance of the copper wire? 12. A cylindrical copper cable carries a current of 1200 A. There is a potential difference of 1.6 X 10- 2 V between two points on the ea· ble that are 0.24 m apart. What is the radius of the cable? 13. In Section 12.3 it was mentioned that temperatures are often measured with electrical resistance thermometers made of platinum wire. Suppose that the resistance of a platinum resistance thermometer is 125 n when its temperature is 20.0 DC. The wire is then immersed in boiling chlorine, and the resistance drops to 99.6 n. The temperature ** 9. ssm A beam of protons is moving toward a target in a particle ae·, celerator. This beam constitutes a current whose value is 0.50 pA (a) How many protons strike the target in 15 s? (b) Each proton has a kinetic energy of 4.9 X 10- 12 1. Suppose the target is a IS-gram block of aluminum, and all the kinetic energy of the protons goes into heating it up. What is the change in temperature of the block that reo suits from the 15-s bombardment of protons? Section 20.3 Resistance and Resistivity 10. ~ The resistance and the magnitude of the current depend on the path that the current takes. The drawing shows three situations in which the current takes different paths through a piece of material. Each of the rectangular pieces is made from a material whose resis- tivity is p = 1.50 X 10- 2 fl· ill, and the unit of length in the drawing is La = 5.00 cm. Each piece of material is connected to a 3.00- V bat· tery. Find (a) the resistance and (b) the current in each case. +,"- 2.0 V -- /4 R 4 + .... - 3.0 V 5.0 V Question 15 R I + .... - -- /1 1" I 1'0 1 ' '·1 /3 t R3 +1 - + +.- LEMS 634 CHAPTER 20 ELECTRIC CIRCUITS Section 20.10 Kirchhoff's Rules 15. When applying Kirchhoff's rules, one of the essential steps is to mark each resistor with plus and minus signs to label how the potential changes from one end of the resistor to the other. The circuit in the drawing contains four resistors, each marked with the associated plus and Section 20.9 Internal Resistance 13. A battery has an emf of V and an internal resistance of r. What resistance R, when connected across the terminals of this battery, will

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## This note was uploaded on 10/04/2009 for the course PHYS 750:204 taught by Professor Rollino during the Spring '09 term at Rutgers.

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Chapter20 - 634 CHAPTER 20 Section 20.9 ELECTRIC CIRCUITS...

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