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CU-Boulder PHYS 1120 - Questions

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11The switch in the circuit is closed at t=0. What is the initial current in theinductor, immediately after theswitch is closed (at t=0+) ?A) 0 A B) 0.5 AC)1.0 A D) 2 AE) None of these.dtdiL!="L=10 H R=20 ΩV=10 V2The switch in the circuit is closed at t=0. What is the initial current in theinductor, immediately after theswitch is closed (at t=0+) ?A) 0 A B) 0.5 AC)1.0 A D) 2 AE) None of these.dtdiL!="L=10 H R=20 ΩV=10 V3CAPA #13 is due FridayNew online participation survey is still up!Reading: 34.3-5_________________________Last: Inductors in circuitsToday: Inductors, and AC circuitsNext: Maxwell's equations, putting it all together!24The switch in the circuit below is closed at t=0.What is the initial rate of change ofcurrent di/dt in the inductor,immediately after the switch isclosed ?A) 0 A/s B) 0.5A/sC)1A/s D) 10A/sE) None of these.Clicker QuestionHints: What is the initial current through the circuit?Given that - what is the initial voltage across the inductor?L=10 H R=20 ΩV=10 V5The switch in the circuit below is closed at t=0.L = 10H V = 10V R=20 Ω Clicker QuestionV=0Before t=0, V=?V=?What is the initial rate of change ofcurrent di/dt in the inductor,immediately after the switch isclosed ?A) 0 A/s B) 0.5A/sC)1A/s D) 10A/sE) None of these.Hints: What is the initial current through the circuit?Given that - what is the initial voltage across the inductor?dtdiL!="6The switch in the circuit below is closed at t=0.L = 10H V = 10V R=20 Ω Clicker QuestionV=0V=0V=?What is the initial rate of change ofcurrent di/dt in the inductor,immediately after the switch isclosed ?A) 0 A/s B) 0.5A/sC)1A/s D) 10A/sE) None of these.Hints: What is the initial current through the circuit?Given that - what is the initial voltage across the inductor?Before t=0,37The switch in the circuit below is closed at t=0.L = 10H V = 10V Clicker QuestionV=0V=0V=10V=10!R=20 ΩWhat is the initial rate of change ofcurrent di/dt in the inductor,immediately after the switch isclosed ?A) 0 A/s B) 0.5A/sC)1A/s D) 10A/sE) None of these.Hints: What is the initial current through the circuit?Given that - what is the initial voltage across the inductor?8The switch in the circuit below is closed at t=0.Clicker QuestionV=0V=10At t=0+,V=?What is the initial rate of change ofcurrent di/dt in the inductor,immediately after the switch isclosed ?A) 0 A/s B) 0.5A/sC)1A/s D) 10A/sE) None of these.Hints: What is the initial current through the circuit?Given that - what is the initial voltage across the inductor?dtdiL!="L = 10V = 10V R=20 Ω9The switch in the circuit below is closed at t=0.L = 10H V = 10V R = 20! Clicker QuestionV=0V=10V=10!!(briefly)What is the initial rate of change ofcurrent di/dt in the inductor,immediately after the switch isclosed ?A) 0 A/s B) 0.5A/sC)1A/s D) 10A/sE) None of these.Hints: What is the initial current through the circuit?Given that - what is the initial voltage across the inductor?410The switch in the circuit below is closed at t=0.L = 10H V = 10V R = 20! Clicker QuestionAnswer: I(initial)=0, so it must still be 0. Thus, ΔV(across R)=0V(across inductor) = V(batt!) , but also V(inductor) = L di/dt.So at t=0+, di/dt = V(batt)/L = 10V/10H = 1 A/s.V=0V=10V=10!!(briefly)What is the initial rate of change ofcurrent di/dt in the inductor,immediately after the switch isclosed ?A) 0 A/s B) 0.5A/sC)1A/s D) 10A/sE) None of these.Hints: What is the initial current through the circuit?Given that - what is the initial voltage across the inductor?dtdiL!="11L = 10H V = 10V R2 = 10Ω R1 = 10Ω An LR circuit is shown below. Initially the switch is open. Attime t=0, the switch is closed. What is the current thru theinductor L immediately after the switch is closed (time = 0+)?A) ZeroB) 1 AC) 0.5AD) None of these.Clicker Question12After a long time, what is the current from the battery?A) 0A B) 0.5A C) 1.0A D) 2.0A E) None of these.L = 10H V = 10V R2 = 10Ω R1 = 10Ω An LR circuit is shown below. Initially the switch is open. Attime t=0, the switch is closed.Clicker Question513AC CircuitsThe Voltage in your wall sockets at home is AC.AC stands for Alternating Current, but would perhaps moreappropriately be called Alternating Voltage.Alternating = Sinusoidal with time14)sin()( tVtVpeak!=Tf!!"22 ==ω is the radial frequency (radians / second)f is the frequency in (cycles / second = Hertz)T is the period in (seconds), i.e. time for one cycle15In the United States of Americaf = 60 cycles/second or HertzT = (1 / 60) secondsVpeak = 170 VoltsOne might be interested in something like the average Voltage.But, the average V(t) = 0.6162square)mean root ( VVVrms==Time Average of Voltage squared.2/2/1)(sin2ppprmsVVtVV ===!Time Average of sin2 or cos2 over many cycles = 1/2VoltsVVrms 1202/170 ==This is how we refer to theUS Standard Voltage.17The term “AC Voltage” or “VAC” means 2/peakrmsVV =The term “AC Current” [somewhat redundant] means2/peakrmsii =RMS values of AC Voltage and Current are always implied ifnot explicitly stated otherwise. This is because the old DCformulas involving V, i, R, P (power) all hold for AC circuits ifwe use the RMS values.18Example: AC Voltage across a resistor~VAC R)sin()( tVtVp!=)sin()sin()( tiRtVRVtipeakp!!===)(sin)(2tViiVtPppeak!==Instantaneous Power is oscillating from zero to maximum.719We might be interested in the average (over time) powerdelivered to the resistor.)(sin)(2tViiVtPpeakpeak!==peakpeakpeakpeakVitVitP21)(sin)(2>=<>=<!!"#$%&!"#$%&>=<peakpeakVitP2121)(rmsrmsaveViP =Same form as before, but now RMS values.21CT 33.35A 100 W light bulb is attached to a wall plug. (120 VAC, 60 Hz)What is the peak power output to the bulb?A)100 WB) Sqrt[2]*100 W = 141 WC) 200 WD) Other22CT 33.36A 600 Watt hairdryer is attached to 120 VACcircuit. What is the peak current through thehairdryer (to within 5%)?A: 0 A B) 5 A C) 7 A D) 10 AE) OtherP = IV, which means P(ave) = I(rms)* V(rms)600 W = I(rms) * 120 V => I(rms) = 600/120 = 5 A.But I(peak) = I(rms)*Sqrt[2] = 5*1.4, about 7.823CT 33.37The instantaneous power consumed by my De-luxe ToasterOven looks like this as a function of time:24CT 33.38Which of the following is correct? P ave V rms I rmsA: 1200 W 120 V 10 A (=1200/120)B: 1200 W 170 V 7 A (=1200/170)C: 600 W 120 V 5 A (= 600/120)D: 600 W 170 V 3.5 A (=600/170)E: None of the above is right.1200 W25CT 33.39What is "T" in the picture (in the


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