ind-1
Pink
A
Yellow
B
Which arrangement of two coils has the larger mutual
inductance?
ind-2
A large-diameter single-turn coil (coil 2) is wrapped around
a long smaller-diameter solenoid (coil 1) as shown.
Φ
Φ
Which is larger: M12 = 1 or M21 = 2 ?
I2
I1
A: M12 > M21
B: M12 < M21
coil 2
C: M12 = M21
D: Not enough info/don't know
coil 1
B) The number of turns in coil 2 is
doubled.
What happens to M = Φ2/I1?
A: M remains constant.
B: M doubles
C: M quadruples
D: None of these/don't know.
ind-3
Inductor 1 consists of a single loop of wire. Inductor 2 is
identical to 1 except it has two loops.
What is the B field in the center of coil 2, B2, compared to
B1?
I
Coil 1
I
A: B2 = B1.
C: B2 = B1/2.
E: None of these
Coil 2
B: B2 = 2B1 .
D: B2=4B1 .
How do the self-inductances of the two loops compare?
(Recall, L = Φ = N BA )
I
A: L2 = 2 L1
C: L2 < 2L1
I
B: L2 > 2L1
.
ind-4
Two long solenoids, each of inductance L, are connected
together to form a single very long solenoid of inductance
Ltotal. What is Ltotal?
A: 2L
+
L
=
B: 4L
C: 8L
L
D: none of these/don't
know
Ltotal = ?
ind-5
An LR circuit is shown below. Initially the switch is open.
At time t=0, the switch is closed. What is the current thru
the inductor L immediately after the switch is closed
(time = 0+)?
R1 = 10Ω
V = 10V
L = 10H
R2 = 10Ω
A: Zero
B: 1 A
C: 0.5A
D: None of these/don't know.
After a long time, what is the current from the battery?
A: Zero
D: 2 A
B: 1 A
C: 0.5A
E: None of these/don't know.
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
A: zero
B: not zero
ind-6
The switch in the circuit below is closed at t=0.
R = 20Ω
V = 10V
L = 10H
What is the initial rate of change of current dI/dt in the
inductor, immediately after the switch is closed ? (Hint:
what is the initial voltage across the inductor?)
A: 0 A/s
B: 0.5 A/s
C: 1 A/s
D: 10 A/s
E: None of these.
ind-7
The same current I is flowing through solenoid 1 and
solenoid 2. Solenoid 2 is twice as long and has twice as
many turns as solenoid 1, and has twice the diameter.
I
1
2
I
(Hint: for a solenoid
B = µo n I )
What is the ratio of the B fields in the solenoids?
B2/B1= ...
A: 1
D: 8
B: 2
C: 4
E: None of these.
What is the ratio of the magnetic energy contained in
solenoid 2 to that in solenoid 1?
U2/U1= ...
AC-1
A light bulb is plugged into a normal (120V, 60Hz, AC)
wall socket. How many times a second is the
instantaneous power output to the bulb equal to zero?
A:
B:
C:
D:
E:
Never, there is always power
30 times a second
60 times a second
120 times a second
None of these.
AC-2
.
A 100W light bulb is plugged into a normal (120V, 60Hz,
AC ) wall socket.
What is the peak power output to the bulb?
A: 100W
2 *100W (= 141W)
B:
C: 200W
D: None of these.
AC-3
The instantaneous power consumed by my
De-luxe Toaster Oven might look like this as a function of
time:
Power (AC)
+1200 W
0
T
time
Which of the following is correct?
P ave
V rms
I rms
A:
1200 W
120 V
10 A (=1200/120)
B:
1200 W
170 V
7A
(=1200/170)
C:
600 W
120 V
5A
(= 600/120)
D:
600 W
170 V
3.5 A (=600/170)
E: None of the above is right.
What is "T" in the picture above (in the USA)?
A: 1/60 s
B: 1/120 s
C: 1/30 s
D: other
AC-4
A 600W hairdryer is attached to 120VAC circuit. What is
the approximate peak current through the hairdryer?
A: 10 A
B: 7 A
C: 5 A
D: ??
AC-5
A transformer is attached to a battery and a resistor as
shown.
The voltage difference across the resistor R is ...
A: V N2/N1
B: V N1/N2
D: zero.
E: not enough info
V
C: V
N2
N
1
R
iron core
AC-6
The primary coil of a transformer is connected to a battery,
a resistor, and a switch. The secondary coil is connected to
an ammeter. When the switch is thrown closed, the
ammeter shows..
A: a zero current
B: a non-zero current for a brief instant
C: a steady non-zero current.
A
V
R
iron core
AC-7
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 100MW.
The engineer decides to double voltage V.
By what factor does the power lost in the cable
(Plost=I2Rcable) decrease?
A: No decrease
Rcable
VAC
B: factor of 2 decrease
I
Rcity
C: factor of 4 decrease
D: factor of 8 decrease
(Hint: if P=IV is fixed, when V goes up, I goes down.)