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Byju's Answer
Standard XII
Physics
The Loudness
The reference...
Question
The reference pressure amplitude
Δ
P
M
0
is often taken to be
3.0
×
10
−
5
N
/
m
2
corresponding to an intensity of
1.0
×
10
−
12
W
/
m
2
. What would the sound level be if
Δ
P
M
were
1
a
t
m
?
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Solution
As we know,
β
(
d
B
)
=
20
l
o
g
Δ
P
M
Δ
P
M
0
then ,
β
(
d
B
)
=
20
l
o
g
1
×
10
5
3.0
×
10
−
5
β
(
d
B
)
=
20
l
o
g
1
3
+
20
l
o
g
(
10
10
)
β
(
d
B
)
=
20
×
(
−
0.4771
)
+
20
×
10
β
(
d
B
)
=
190.46
decibels.
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0
Similar questions
Q.
Show that the sound level,
β
, can be written in terms of the pressure amplitude,
Δ
P
M
, as
β
(
d
B
)
=
20
log
Δ
P
M
Δ
P
M
0
where
Δ
P
M
0
is the pressure amplitude at some reference level.
Q.
The faintest sound that can be heard has a pressure amplitude of about
4
×
10
−
5
N/m
2
and the loudest that can be heard without pain has a pressure amplitude of about
2.8
N/m
2
. Determine the intensity of the faintest sound (both in
W/m
2
and in
dB
).
[Assume, air density is
1.3
kg/m
3
and velocity of sound is
330
m/s
and take
log
10
1.86
=
0.269
]
Q.
In expressing sound intensity, we take
10
−
12
W
/
m
2
as the reference level. For ordinary conversation, the intensity level is about
10
−
6
W
/
m
2
. Expressed in decibel, this is
Q.
The pressure amplitude in a medium through which sound is travelling is
1.5
×
10
−
3
N/m
2
and intensity is
10
−
6
W/m
2
. If the pressure amplitude is increased to
4.5
×
10
−
3
N/m
2
by increasing the volume of sound then the intensity will be
Q.
In expressing sound intensity, we take
10
−
12
W
/
m
2
as the reference level. For ordinary conversation, the intensity level is about
10
−
6
W
/
m
2
. Expressed in decibel, this is
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