Physics 7B
WS C4 (rev. 2.0)
Page 1
C4. AC Circuits  Impedance
V
(
t
)
=
ZI
0
sin
"
t
#
$
( )
I
(
t
)
=
V
0
Z
sin
t
+
#
( )
Questions for discussion
1
. An AC source of frequency
ω
is placed across a resistor with resistance R. Use the loop rule to
find the impedance, Z
R
, and phase angle,
ϕ
R
of a resistor.
2.
An AC source of frequency
ω
is placed across a capacitor with capacitance C. Use the loop rule to
write a differential equation for the charge on the capacitor and solve it. Use your solution to find
the impedance, Z
C
, and phase angle,
C
of a capacitor. (Hint:
cos(
)
=
sin(
+
2
)
)
3.
Qualitatively,why does the impedance of a capacitor increase when the driving frequency of the
source is decreased?
4.
An AC source of frequency
ω
is placed across an inductor with inductance L. Use the loop rule to
write a differential equation for the current through the inductor and solve it. Use your solution to
find the impedance, Z
L
, and phase angle,
L
of an inductor. (Hint:
"
cos(
)
=
sin(
"
2
)
)
5.
Qualitatively,why does the impedance of an inductor increase when the driving frequency of the
source is increased?
6.
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 Fall '10
 yildiz
 Physics, Alternating Current, Electrical impedance, LRC, series LRC circuit, AC Source

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