Physics 340 Fall 2003
EXAM 2
Each Problem is worth
14
points.
1. A dish antenna with a diameter of 20 m completely absorbs a radio wave which strikes
it at normal incidence. The radio wave is a sinusoidal plane wave with electric field
of magnitude
0
0.4
/
.
E
V
m
m
=
a.
What is the amplitude of the magnetic field of this wave?
b.
What is the intensity of the radio wave?
c.
How much energy is absorbed by the antenna in 10 seconds?
2. A transverse traveling wave propagates on a string according to the expression
( , )
(0.35
)sin(10
3
/4)
y x t
m
t
x
p
p
p
=

+
a.
What is the velocity of the wave? (Give speed and direction)
b.
What are the wavelength and frequency?
c.
What is the maximum magnitude of the transverse velocity of the string?
3. The sound level at a distance of 3 m from a source is 120 dB. At what distance will the
sound level be 10 dB?
4. A right circularly polarized EM wave:
0
0
ˆ
ˆ
( , )
cos(
4)
sin(
4)
R
E
z t
E
kz
wt
i
E
kz
wt
j
p
p
=

+
+

+
r
overlaps with a left circularly polarized EM wave:
0
0
ˆ
ˆ
( , )
cos(
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