EE 215 Practice Exam 3
May 29, 2001
(As before, this practice exam has not been controlled for time or dependency on prior
answers.)
Topics
1 (3 points)
a. A device that converts from electromagnetic radiation to electrical values (voltage and
current) is called a(n) __________________.
b. In radar, the doppler effect can tell you the
______________________________.
c. The range of frequency that can be sent over a channel is called
____________________.
2. (First order circuit with exponential forcing function).
In the circuit of figure P2, the source has the form
()
≥
<
=
−
0
10
0
10
4
t
V
e
t
V
t
v
t
s
a. Find the current
i
for t
≥
0.
b. Find the inductance needed so that 99% of the natural response of the circuit is
complete in 100 ms.
3. (Second order circuit)
a. Write the differential equation for the voltage
v
in the
circuit of figure P3 in terms of
i
s
, R, C and L. (Assume
i
s
is constant for t
≥
0.)
b. Suppose that source current
i
s
is not constant, but
rather gives rise to a forcing function of the form 3sin4
t
.
Further, suppose values of R, C and L are chosen so the
characteristic equation is
0
3
5
.
2
5
.
0
2
=
+
+
s
s
. Write the
form of the forced response. Find the coefficients of the forced response.
c. If the characteristic equation of the circuit is
0
5
2
2
=
+
+
s
s
, and the source is
A
t
u
i
s
−
=
1
, find the complete response of the circuit for t
≥
0. Evaluate all
coefficients.
d. If the values of R, L and C are
20
Ω
, 10mH and 300nF, respectively, and the source is
A
t
u
i
s
−
=
1
, how much energy will be dissipated in the resistor during the time t
≥
0?
4. Steady state AC circuit
a. AC voltage measurements are taken on the circuit of figure P4. They are:
v
s
= 120.V
Figure P2
+

100 mH
1
Ω
v
s
i
Figure P3
i
s
R
v
+

L
C
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R
= 82.0V
v
X
= 87.6V
Mystery component X is known (don't ask how!) to
be a capacitor or an inductor. Does KVL hold?
Explain.
b. Using your parts kit, you insert a capacitor in
series with X.
v
R
goes down. Is X a capacitor or an
inductor? Explain your answer.
c. If X is an inductor (which might not be the
answer to part b) of 10mH, and R is 100
Ω
, and you
obtained the measurements in part a, what is the
frequency of the source?
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 Spring '05
 Unknown
 Electrical Engineering, Energy, Alternating Current, Electromagnet, Volt, Resistor, dt, Electrical impedance

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