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Inductors 8 CT 33.28 The switch is closed at t=0. What is the current through the resistor, at t=0+ ? R = 20Ω A) 0 A V = 10V B) 0.5 A C) 1 A D) 10 A E) other L = 10H Inductors 10 CT 33.29 The switch is closed at t=0. What is the current through the resistor after a very long time? R = 20Ω A) 0 A V = 10V B) 0.5 A C) 1 A D) 10 A E) other L = 10H Inductors 13 CT 33.30 At time t=0, the switch is closed. What is the current thru the inductor L just after the switch is closed (t= 0+)? R1 = 10Ω V = 10V A: 0 A B) 0.5 A L = 10H C) 1.0 A R2 = 10Ω D) other Inductors 14 CT 33.31 At time t=0, the switch is closed. What is the current thru the inductor L after a long time? R1 = 10Ω V = 10V A: 0 A B) 0.5 A L = 10H C) 1.0 A R2 = 10Ω D) other Inductors 15 CT 33.32 Now suppose the switch has been closed for a long time and is then opened. Immediately after the switch is opened, the current thru R2 is R1 = 10Ω V = 10V A: 0 A L = 10H B) Not 0 amps. R2 = 10Ω Inductors 16 Now suppose the switch has been closed for a long time and is then opened rapidly. Immediately after the switch is opened, what is the potential difference across the inductor, εL? R1 = 10Ω V = 10V A) B) C) D) L = 10H 0V 1V 10 V Very large R2 = 10Ω CL and RCL circuits • similar to mechanical harmonic oscillator (kinetic and pot AC circuits 1 What is the average power dissipated by the resistor? A) zero B) positive C) negative D) Not enough information AC circuits 2 A light bulb is attached to a wall plug. (120 VAC, 60 Hz) How many times a second is the instantaneous power output to the bulb equal to zero? A: Never, there is always power B: 30 times/sec C: 60 times/sec D: 120 times/sec E: Other AC circuits 3 A 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 W B) Sqrt[2]*100 W = 141 W C) 200 W D) Other AC circuits 4 A 600 Watt hairdryer is attached to 120 VAC circuit. What is the peak current through the hairdryer (to within 5%)? A) 0 A B) 5 A C) 7 A D) 10 A E) Other ©University of Colorado, Boulder AC circuits 5 An electrical engineer at a power plant wants to reduce the energy wasted during power transmission from the plant to the city. The power output Po=IV of the plant is fixed at 100 MW. The engineer decides to double Voltage V. By what factor does the power lost in the cable (Plost=I2Rcable) decrease? A) No decrease B) 2x C) 4x D) 8x ©University of Colorado, Boulder AC circuits 6 A transformer is attached to a battery and a resistor as shown. The voltage difference across the resistor R is ... V N2 N1 R A) V B) V N1/N2 C) V N2/N1 D) 0 E) Other iron core AC circuits 7 A step-down transformer is attached to an AC voltage source and a resistor. How does IR compare to the current that is drawn from the AC source I(in) II(input) in A) IR > I(input) B) IR < I(input) IR IR C) IR = I(input)