PRACTICE EXAMINATION
25 April 2014
United States Naval Academy
Electrical Engineering Department
EE 372
Practice Exam 3
25 April 2014
1. Present your work completely and legibly to receive partial credit. You must show sufficient
steps to justify intermediate results as well as final answers.
2. Put all your work on the exam. If you need more space than that provided, ask your instructor
for paper. Write your answer clearly and use appropriate units. You have 1 hour and 50 minutes
to work this examination.
Problem
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2
3
4
Questions
Total
Value
Score
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PRACTICE EXAMINATION
25 April 2014

(1) The plates of a parallel-plate capacitor have areas of 10 cm2 and are separated by 2 cm. The
capacitor is filled with a dielectric material with a dielectric constant of 4 and the voltage across
it is V (t )  30 cos(2  10 6 t ) V. Find the displacement current.
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PRACTICE EXAMINATION
25 April 2014

(2) A uniform plane wave propagating in a nonmagnetic medium with dielectric constant 2.25

and described by the following equation: E ( y, t )  zˆ 10 cos(2  1010 t  314 y  30) V/m is
incident on a perfect nonmagnetic dielectric medium with a dielectric constant of 1. (Assume
normal incidence.)
(If applicable, results must be stated numerically for full credit)
(a)
(b)
(c)
(d)
(e)
Find the phase velocity associated with the incident wave.
Find the wavelength associated with the incident wave.
Find the intrinsic impedance of the material associated with the incident wave.
Find the phasor representing the incident magnetic field wave.
Find the phasor representing the transmitted electric field wave
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PRACTICE EXAMINATION
25 April 2014

(3) The electric field of a uniform plane wave propagating in free space is given by

E ( z, t )  xˆ5 cos(2  109 t  10z)  yˆ 5 cos(2  109 t  10z  90) V/m
(a) Find the modulus of the electric field.
(b) Find the inclination angle.
(c) Identify the polarization state of the electric field. (Explain your reasoning for full credit.)
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PRACTICE EXAMINATION
25 April 2014

(4) A 100 MHz uniform plane wave traveling in air with average power density 1000W/m2 is
normally incident on a very thick(semi-infinite) glass block with  r  9 that is coated with a
protective dielectric coating of thickness 0.3m with  r  4 as modeled below. Find the average
power density reflected by the coating using a transmission line analogue. (You must use a
transmission line analogue to receive credit for this problem). All media are nonmagnetic
materials.

Air
r=1
0.3m
Coating
r=4
Glass
r=9
Sr AVG=?
Si AVG=1000W/m2
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PRACTICE EXAMINATION
25 April 2014
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Questions
(1) Under what circumstances can a magnetic field produce an electric field?
(2) What is a "uniform plane wave". Specifically discuss the electric and magnetic fields for such
a wave.
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~
(3) Name one assumption we made in order to derive the following equation:  2 E  k 2 E  0
(4) What is a “ray” ?
(5) What does Lenz’s Law describe?
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PRACTICE EXAMINATION
25 April 2014
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