29_Lec-18

29_Lec-18 - Physics 241 Lecture 18 Y E Kim Chapter 29...

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Physics 241 Lecture 18 Y. E. Kim October 28, 2010 Chapter 29, Sections 8-10 October 28, 2010 University Physics, Chapter 26 and 27 1
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± RC Circuits (from Chapter 26) ± RL Circuits ± Energy and Energy Density of a Magnetic Field ± Application to Information Technology October 28, 2010 Physics for Scientists & Engineers 2, Chapter 26 2
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October 28, 2010 University Physics, Chapter 26 3 RC Circuits (from Chapter 26) ± Consider a circuit with a source of emf, V emf , a resistor R , and a capacitor C ± We then close the switch, and current begins to flow in the circuit, charging the capacitor ± The current is provided by the source of emf, which maintains a constant voltage When the capacitor is fully charged, no more current flows in the circuit ± When the capacitor is fully charged, the voltage across the plates will be equal to the voltage provided by the source of emf and the total charge q tot on the capacitor will be tot = CV emf
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October 28, 2010 University Physics, Chapter 26 4 Capacitor Charging (1) ± Going around the circuit in a counterclockwise direction we can write ± We can rewrite this equation remembering that i = dq / d t ± The solution of this differential equation is ± « ZKHUH q 0 = CV emf and W = RC 0 e m f R C V iR ±± ± ± ² ³ ² 0 () 1 ± §· ± ¨¸ ©¹ The term V c is negative since the top plate of the capacitor is connected to the positive - higher potential - terminal of the battery. Thus analyzing counter-clockwise leads to a drop in voltage across the capacitor!
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October 28, 2010 University Physics, Chapter 26 5 Capacitor Charging (2) ± We can get the current flowing in the circuit by differentiating the charge with respect to time ± The charge and current as a function of time are shown here ( W = RC ) t e m f V dq i d R §· ± ¨¸ ©¹ 0 () 1 q ± ± Math Reminder:
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October 28, 2010 University Physics, Chapter 26 6 ± 1RZ OHW·V WDNH D UHVLVWRU R and a fully charged capacitor C with charge q 0 and connect them together by moving the switch from position 1 to position 2 ± In this case, current will flow in the circuit until the capacitor is completely discharged ± While the capacitor is discharging we can apply the Loop Rule around the circuit and obtain
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This note was uploaded on 09/09/2011 for the course PHYS 241 taught by Professor Wei during the Fall '08 term at Purdue.

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29_Lec-18 - Physics 241 Lecture 18 Y E Kim Chapter 29...

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