Lect11 - Physics 212 Lecture 11 Today's Concept: RC...

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Physics 212 Lecture 11, Slide 1 Physics 212 Lecture 11 Today's Concept: RC Circuits (Circuits with resistors & capacitors & batteries)
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Music Who is the Artist? A) Miles Davis B) Wynton Marsalis C) Chris Botti D) Nina Simone E) Chet Baker Ultimate West Coast Cool Jazz from the 50’s Definitive version of My Funny Valentine Hypnotizing voice… DVD Must-See: Twilight of his career/life Interviewed by Elvis Costello (Diana Krall’s husband) Van Morrison does “Send in the Clowns” Physics 212 Lecture 11
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Physics 212 Lecture 11, Slide 3 Your Comments 05 “WHERE ARE THE GRADES??? Lazy TA's in my opinion. In phys 211 we got our grades the next day. ..” “The relationship between time and resistor over a short time and over a long time.” “I do not understand why it changes over a long time.” “the last question on two loop RC circuit” We’ll emphasize the limiting cases I don't think this was too bad. It sucks that we will have to memorize the equations for q(t) and I(t) though Remember that I = dq/dt You need to know the solution to one differential equation (exponential) “My friends and I discussed and we are not sure if we RCing the concepts right. We may just have to throw in the Tau-el.”
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Physics 212 Lecture 11, Slide 4 Today’s Plan: 1) Examples with switches closing and opening - What changes? - What is constant? 2) Example problem 3) Exponentials Key Concepts: 1) Understanding the behavior of capacitors in circuits with resistors 2) Understanding the RC time constant 07
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The 212 Differential Equations • We describe the world (electrical circuits, problems in heat transfer, control systems, etc., etc.) using differential equations • You only need to know the solutions of two basic differential equations Physics 212 Lecture 11, Slide 5 / 0 1 0 t dq q q q e dt τ - + = = ( ) 2 2 0 2 0 sin d q q q q t dt ω φ + = = +
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Physics 212 Lecture 11, Slide 6 RC Circuit (Charging) • Kirchoff’s Voltage Rule • Short Term (q = q 0 = 0) • Long Term (I c =0) R V battery C a b battery q -V + +IR = 0 C - + + = 0 0 0 battery V I R battery 0 V = R - + + = 0 0 battery q V R C = battery q CV Intermediate - + + = 0 battery q dq V R C dt - = - / ( ) (1 ) t RC q t q e - = / 0 ( ) t RC I t I e 11 a R V battery C b • Capacitor uncharged, Switch is moved to position “a”
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Physics 212 Lecture 11, Slide 7 13 Checkpoint 1a Checkpoint 1b Close S1, V 1 = voltage across C immediately after V 2 = voltage across C a long time after A) V 1 = V V 2 = V B) V 1 = 0 V 2 = V C) V 1 = 0 V 2 = 0 D) V 1 = V V 2 = 0 A circuit is wired up as shown below. The capacitor is initially uncharged and switches S1 and S2 are initially open. “There is no voltage at the get go.” “There is no current, so the resistor has no voltage drop” “As time progress, the voltage will drop to 0 since the current goes to 0” “The capacitor is completely charged and doesn't allow any current to flow so no voltage can drop across the resistor. All voltage must drop across the capacitor” Checkpoint 1a
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This note was uploaded on 03/12/2012 for the course PHYS 212 taught by Professor Kim during the Fall '08 term at University of Illinois, Urbana Champaign.

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Lect11 - Physics 212 Lecture 11 Today's Concept: RC...

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