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Learning Object 1

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Measuring sound levels lo4
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Learning Object 1

  1. 1. 11350148 Activity ID : 679 Lab: L2H -Blue Physics 101 Learning Objective Topic 15.6 Measuring Sound Levels DECIBELS
  2. 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?
  3. 3. Formula We use this to express sound intensity levels
  4. 4. Formula - Sound intensity level (dB) - Reference level (1000Hz for sound) -Initial intensity (W/m2) -Intensity at B(I) (W/m2)
  5. 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. 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. 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. 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. 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. 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. 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. 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. 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

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