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8B Worksheet Answers
10. AC Circuits
1. For this problem,
Graph A
represents
I
R
(
t
), and the battery has a frequency of 398 Hz.
This frequency is the
f
of the problem, but our formulas will typically use the
angular
frequency
,
ω
. The relationship between
f
and
ω
is
ω
= 2
π
f
= 2500 Hz.
a) i)
The potential and current are
in phase
across a resistor, so
Graph D
best
represents
V
R
(
t
).
ii) This is a
series
circuit, so the current is the same everywhere throughout the
circuit. Therefore,
Graph A
best respresents
I
C
(t).
iii) The potential difference across a capacitor
lags
the current by a quarterperiod
(or by
π
/2, or by 90
°
, depending on how you prefer to express these things!).
Therefore,
Graph B
best represents
V
C
(
t
).
b)
X
C
= 1 /
ω
C
= 40
Ω
c)
Z
=
R
2
+
X
C
2
= 50
Ω
d)
I
rms
=
V
batt,rms
/
Z
= 0.24 A
e) i)
V
R,rms
=
I
rma
R
= 7.2 V
ii)
V
C,rms
=
I
rms
X
C
= 9.6 V
f) The answers don’t add up because the two voltages are not in phase.
2. For this problem,
Graph A
represents
I
R
(
t
), and the battery has a frequency of 398 Hz.
This frequency is the
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 Spring '10
 CatherineBordel
 Physics, Work

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