ps11

ps11 - MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of...

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PS11-1 MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Physics 8.02 Fall 2008 Label with your name, table number and group. Turn in at the homework box. Problem Set 11 Due: Thursday, November 20 th at 12:00 pm Warm Up… Problem 1: Where’s the energy go? Consider a simple RC circuit consisting of a “variable” battery (EMF 0 V or ε ), a resistor R and an uncharged capacitor C all in series. At time t=0 the battery is “turned on” (EMF ε ) and the capacitor is allowed to charge. A time T (>> RC ) later the battery is turned off (EMF 0 V) and the capacitor discharges. This process is continually repeated. (a) How much energy does the resistor dissipate while the capacitor is being charged (i.e. between t=0 and t= T )? (b) How does this compare to the amount of energy stored in the capacitor at time T ? (c) How much energy does the resistor dissipate while the capacitor is discharging (i.e. between t= T and t=2 T )? (d) What is the time average power dissipated by the resistor? Hint: To average a set of numbers you add the numbers and divide by the number you added. To average a periodic function, integrate it over one period and divide by the length (or in this case time ) of the period. Problem 2: LC Circuit (a) Initially, the capacitor in a series LC circuit is charged. A switch is closed, allowing the capacitor to discharge, and after time T the energy stored in the capacitor is one- quarter its initial value. Determine L if C and T are known. (b) A capacitor in a series LC circuit has an initial charge 0 Q and is being discharged. Find, in terms of L and C , the flux through each of the N turns in the coil at time t , when the charge on the capacitor is Q ( t ). (c) An LC circuit consists of a 10.0-mH inductor and a 0.100- F µ capacitor. If the maximum instantaneous current is 0.200 A, what is the greatest potential difference across the capacitor?
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PS11-2 Sample Exam Problem…
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This note was uploaded on 02/22/2009 for the course 8 02 taught by Professor Sciolla during the Fall '08 term at MIT.

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ps11 - MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of...

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