PHY132 Final
Practice Exam
Solutions:
1)
Consider an LRC series circuit connected to a 60 Hz AC voltage source with a peak voltage of
51 V. The circuit contains an inductance of L = 230 mH, a resistor of R = 200
Ω
, and a
capacitor of C = 15
µ
F.
a)
What is the impedance Z in this series LRC circuit?
Ω
=
ω
−
ω
+
=
=
π
=
ω
219
C
1
L
R
Z
s
rad
377
f
2
2
2
b)
What is the average power being dissipated in the circuit?
W
4
.
5
Z
2
RV
Z
R
2
Z
V
2
V
cos
I
V
P
2
2
0
0
0
rms
rms
=
=
×
×
=
φ
=
c) How would you change the value of the inductance L to maximize the average power
dissipation?
mH
469
C
1
L
C
1
L
minimal
being
for Z
maximal
is
P
2
=
ω
=
⇒
ω
=
ω
⇒
2) An LRC series circuit with R = 250
Ω
, L = 0.400 H, and C = 20.0 nF, is connected to an AC
voltage source of 65 V, operating at the resonance frequency of the circuit.
a)
What is this resonance frequency of the circuit?
s
rad
11180
LC
1
0
=
=
ω
b) What is the current in the circuit?
A
26
.
0
R
V
Z
V
I
resonance
at
R
Z
rms
rms
rms
=
=
=
⇒
=
c)
What is the voltage on the capacitor?
V
1160
C
I
V
rms
C
=
ω
=
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3) The virtual image of an object in a spherical mirror is at a distance of 35 cm from the object.
The image is upright and six times larger than the object.
a) Draw the ray diagram.
o
i
b)
What is the distance between the object and the mirror?
cm.
5
is
mirror
and
object
between
distance
The
cm
30
d
cm
5
d
d
7
d
d
cm
35
d
6
d
i
o
o
i
o
o
i
−
=
⇒
=
⇒
=
−
=
−
=
c)
What is the radius of curvature of the mirror?
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 Fall '04
 Rijssenbeek
 Physics, Inductance, Light, AC voltage source, LRC series circuit

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