pan (zp695) – ch25h1 – chiu – (56565)
1
This
printout
should
have
27
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001 (part 1 of 2) 10.0 points
A particular AM radio station broadcasts at
a frequency of f= 900 kHz.
What is the
wavelength of this electromagnetic radiation?
Remember that
c
= 3
×
10
8
m
/
s
.
Correct answer: 333
.
333 m.
Explanation:
Applying
λ
=
c
f
,
λ
=
c
f
=
3
×
10
8
m
/
s
9
×
10
5
Hz
= 333
.
333 m
002 (part 2 of 2) 10.0 points
How much time is required for the radiation
to propagate from the broadcasting antenna
to a radio d = 11
.
5 km away?
Correct answer: 3
.
83333
×
10

5
s.
Explanation:
Noting that d = c
Δ
t
,
Δ
t
=

r

c
Δ
t
≈
11500 m
3
×
10
8
m
/
s
≈
3
.
83333
×
10

5
s
003
10.0 points
Consider
the
two
examples
of
the
cosine
curves displayed in the figure below.
Study
the two curves, and make sure you under
stand the relationship between them. Choose
the graph that correctly displays the plot of
E
cos
2
π
t
T
+
π
.
E
cos
2
π
t
T
E
cos
2
π
t
T
+
π
2
t
=0
T
2
T
t
t
1.
t
=0
T
2
T
t
2.
t
=0
T
2
T
t
correct
3.
t
=0
T
2
T
t
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pan (zp695) – ch25h1 – chiu – (56565)
2
4.
t
=0
T
2
T
t
Explanation:
The graph of
E
cos
2
π
t
T
+
π
has a mini
mum value of E when
t
takes on values of zero
and even multiples of T/2. It has a maximum
value of E when
t
takes on odd multiples of
T/2. To be
out of phase
means that the two
graphs reach their maximums and their mini
mums at di
ff
erent times.
004 (part 1 of 7) 10.0 points
The height of a particular water wave is de
scribed by the function
y
=
A
cos
B t

C x
+
π
2
,
where
A
= 1
.
19381 m
B
= 2
.
38761 s

1
C
= 0
.
477522 m

1
.
Determine the angular frequency
ω
.
Correct answer: 2
.
38761 s

1
.
Explanation:
Note that the general form of this equation
is:
y
=
A
cos(
ω
t

kx
+
φ
) where
k
= 2
π
/
λ
is called the wavenumber.
(Note that in
spectroscopy, wavenumber is defined as 1
/
λ
,
so chemists generally use this definition of
wavenumber.)
Based on the general form of the equation,
we can see that the angular frequency multi
plies
t
, so in this case
ω
=
B
=
2
.
38761 s

1
.
You could also have deduced this through unit
analysis.
B
is the only number that has the
units of frequency.
005 (part 2 of 7) 0.0 points
WITHDRAWN
006 (part 3 of 7) 0.0 points
WITHDRAWN
007 (part 4 of 7) 10.0 points
Determine the wavelength
λ
.
Correct answer: 13
.
1579 m.
Explanation:
We know that
k
must be given by
C
above,
because in the general form of the equation
k
multiplies
x
. And since 2
π
/
λ
=
k
, we have
2
π
λ
= 0
.
477522 m

1
so,
λ
=
13
.
1579 m
008 (part 5 of 7) 0.0 points
WITHDRAWN
009 (part 6 of 7) 10.0 points
What is the direction of propagation.
1.
+x direction
correct
2.
Neither
3.

x direction
Explanation:
The direction of propogation is +x direc
tion because the sign in (
ω
t

kx
) is negative.
010 (part 7 of 7) 10.0 points
At (
x, t
) = (0
,
0), what is the amplitude of the
wave?
Correct answer: 0 m.
Explanation:
At (
x, t
) = (0
,
0),
y
=
Acos
π
2
.
Thus, the
height of the wave at
x
= 0 and
t
= 0 is zero.
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 Spring '08
 Turner
 Magnetic Field, Correct Answer, ch25h1 chiu

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