2. Decibel (dB): A logarithmic unit used for comparisons of
power or intensity
However, logarithmic scales are RELATIVE and thus, need a
reference level
In terms of sound, the reference level (OdB)
is 1000Hz
This is because humans cannot hear anything below this
frequency
What is it?
4. Formula
- Sound intensity level (dB)
- Reference level (1000Hz for sound)
-Initial intensity (W/m2)
-Intensity at B(I) (W/m2)
5. 1. There is still sound at 0 decibels
2. We can say that changes in wavelengths of sounds are
measured in decibels
Quick Questions T/F
6. 1. There is still sound at 0 decibels
2. We can say that changes in wavelengths of sounds are
measured in decibels
Quick Questions T/F
Hints:
1. What IS 0 decibels?
2. Look at the formula, and try to figure out what
decibels measure through the units used.
7. 1. There is still sound at 0 decibels
2. We can say that changes in wavelengths of sounds are
measured in decibels
Quick Questions T/F
Answers:
1. True
There is still sound at 0 decibels because 0dB is the
reference level. Remember that for sound, the reference
level (0dB) is1000Hz
2. False
When we look at the formula, the units W/m2 cancels out,
leaving us with Hertz from the reference level. There is
no way that hertz is the unit of wave lenghts, and thus
this is false.
8. A PHYS 101 student estimates that the sound intensity of a
Koerner library is 7 times that of the sound intensity of her
quiet bedroom at night. If the difference between the β of the
library and her bedroom is 10dB, is she right?
Longer Question
9. A PHYS 101 student estimates that the sound intensity of a
Koerner library is 7 times that of the sound intensity of her
quiet bedroom at night. If the difference between the β of the
library and her bedroom is 10dB, is she right?
Longer Question
1. Note the useful information given
Delta β is 10 dB
10. A PHYS 101 student estimates that the sound intensity of a
Koerner library is 7 times that of the sound intensity of her
quiet bedroom at night. If the difference between the β of the
library and her bedroom is 10dB, is she right?
Longer Question
1. Note the useful information given
Delta β is 10 dB
2. Write out the formula
11. A PHYS 101 student estimates that the sound intensity of a
Koerner library is 7 times that of the sound intensity of her
quiet bedroom at night. If the difference between the β of the
library and her bedroom is 10dB, is she right?
Longer Question
1. Note the useful information given
Delta β is 10 dB
2. Write out the formula
3. Since we know Delta β is 10 dB, we can simply plug it
in. Also, as I needs to be greater than I0 in order to
obtain a positive number, we can also substitute I as
the library and I0 as the room. We also ignore 0dB
10 dB = 10log10[ Ilibrary/ Iroom ]
12. A PHYS 101 student estimates that the sound intensity of a
Koerner library is 7 times that of the sound intensity of her
quiet bedroom at night. If the difference between the β of the
library and her bedroom is 10dB, is she right?
Longer Question
4. Rearrange to find the relationship between ILibrary and
Iroom
10 dB = 10log10[ Ilibrary/ Iroom ]
1dB = log10[ Ilibrary/ Iroom ]
101 = [ Ilibrary/ Iroom ]
10dB Iroom = Ilibrary
13. A PHYS 101 student estimates that the sound intensity of a
Koerner library is 7 times that of the sound intensity of her
quiet bedroom at night. If the difference between the β of the
library and her bedroom is 10dB, is she right?
Longer Question
4. Rearrange to find the relationship between ILibrary and
Iroom
10 dB = 10log10[ Ilibrary/ Iroom ]
1dB = log10[ Ilibrary/ Iroom ]
101 = [ Ilibrary/ Iroom ]
10dB Iroom = Ilibrary
This tells us that the sound intensity of the library, is
equivalent to 10 times the sound intensity of the room (in
dB), NOT 7.
Thus, the student is wrong
