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)