Phy122_0930 - ch. 19

Phy122_0930 - ch. 19 - Physics 122 Sept 30 2010 Starting...

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Physics 122 Sept. 30, 2010 Starting chapter 19. This material will not appear on your 1 st midterm exam. yu r mr mm . October 4. Review session: Javits 103, 6:50-8:50 PM ctober 5 Second lecture on Ch 19 October 5. Second lecture on Ch. 19 October 5. 8:30-10:00 PM Midterm exam on Ch. 15-18. Last names beginning A-J: Old Engineering 145 Last names beginning K-Z: Old Chem. 116 Bring a calculator, pencils, erasers, 1 8½” x 11” page of notes (both sides OK). October 6. 5:00 PM. HW on Ch. 19 is due. Question 1:

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Resistor Capacitor circuits. apacitor initially uncharged is Capacitor, initially uncharged, is charged through a resistor once the switch is closed. he voltages across each The voltages across each component and the current in the circuit have an exponential time dependence. I(t) = V Batt R e t / RC (t) = / C = (1 / ) t / RC(dimensionless) Æ
Question 2: If the time onstant of the top constant of the top circuit is 1 msec., what is the time onstant of the constant of the bottom circuit? (Each R and each C is identical to the nes in the top ones in the top circuit.)

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Question 2: f the time If the time constant of the top circuit is 1 msec., what is the time constant of the bottom circuit? R bottom = R top / 3 3 C bottom = 3 C top So R bottom bottom = R top top
I(t) = V Batt R e t / RC / (t) C = (1 / ) uestion #3 In an RC circuit with 100 Volts C = Question #3 : In an RC circuit with V batt = 100 Volts, C = 1 μ F, R = 100 , what is the capacitor voltage 100 μ sec after the switch is closed?

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Question #3: In an RC circuit (R = 100 Ohm, C = 1 μ F, V = 100 Volts what is the capacitor voltage 100 ec 100 Volts ) , what is the capacitor voltage 100 μ sec after the switch is closed? V ap = 100 (1 - e - t / RC ) cap t/RC= 1.0x10 -4 / (100 x 1x10 -6 ) = 1 100 (1 – -1 = 100 (1 – 368) = 63 2 Volts cap = 100 (1 e ) = 100 (1 0.368) = 63.2 Volts After 200 μ sec (total), t/RC = 2, cap = 100 (1 – e -2 ) = 100 (1 – 0.136) = 86.4 Volts After 300 μ sec (total), t/RC = 3, cap = 100 (1 – e -3 ) = 100 (1 – 0.0498) = 95.0 Volts
You can also go the other way. Given the desired value, V R (t) / V Batt , find t/ R C. V (t)/V = e t / RC / ln[V (t) /V ] = ln[e ] = t/RC o take the

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Phy122_0930 - ch. 19 - Physics 122 Sept 30 2010 Starting...

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