kuehner (rjk679) – HW15 – Mackie – (20211)
1
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001
10.0 points
Sound level
β
in decibels is defined as
β
≡
10 log
parenleftbigg
I
I
0
parenrightbigg
,
where
I
0
= 1
×
10
−
12
W
/
m
2
.
The decibel
scale intensity for busy traffic is 80 dB. Two
people having a loud conversation have a deci
bel intensity of 70 dB.
What is the approximate combined sound
intensity?
Correct answer: 0
.
00011 W
/
m
2
.
Explanation:
Let :
β
1
= 80 dB
,
β
2
= 70 dB
,
and
I
0
= 1
×
10
−
12
W
/
m
2
.
I
=
I
0
10
β/
10
,
so the combined sound intensity
I
is
I
=
I
1
+
I
2
=
I
0
parenleftBig
10
β
1
/
10
+ 10
β
2
/
10
parenrightBig
= (1
×
10
−
12
W
/
m
2
)
(
10
8
+ 10
7
)
=
0
.
00011 W
/
m
2
.
002
(part 1 of 2) 10.0 points
Two sound sources radiating in phase at a fre
quency of 560 Hz interfere such that maxima
are heard at angles of 0
◦
and 20
◦
from a line
perpendicular to that joining the two sources.
The velocity of sound is 340 m/s.
y
L
d
S
1
S
2
θ
listening
direction
θ
δ
Assume:
L
≫
d
Find
the
separation
between
the
two
sources.
Correct answer: 1
.
77517 m.
Explanation:
Let :
f
= 560 Hz
,
v
= 340 m
/
s
,
θ
1
= 0
◦
,
and
θ
2
= 20
◦
.
r
2
r
1
y
L
d
S
1
S
2
θ
= tan
−
1
parenleftBig
y
L
parenrightBig
listening
direction
δ
≈
d
sin
θ
≈
r
2
−
r
1
P
O
negationslash
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 Spring '09
 MIHALISIN
 Physics, Frequency, Wavelength, Decibel, m/s, vamb

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