12.2 Physics 6B Decibels and Doppler Effect

12.2 Physics 6B Decibels and Doppler Effect - Physics 6B...

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Unformatted text preview: Physics 6B Decibels and Doppler Effect Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB Sound Intensity and Decibel Level Formulas: Basic rule of thumb: for each factor of 10 change in intensity, add or subtract 10 dB 2 m W 12 2 10 I ; I I log 10 r 1 I- = = Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB Sound Intensity and Decibel Level How to calculate decibels from intensity: Suppose a sound has intensity I=10-3 W/m 2 . To find the Intensity Level (in dB) we can use the definition: How to calculate intensity from decibels: Suppose a sound has a sound level of 73 dB. To Find the intensity (in W/m 2 ) we use the definition again: Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB dB 90 ) 10 log( 10 10 10 log 10 10 I ; I I log 10 9 m W 12 m W 3 m W 12 2 2 2 = = = = = --- 2 2 2 2 2 2 2 m W 5 m W 5 3 . m W 12 7 3 . m W 12 3 . 7 m W 12 m W 12 m W 12 10 2 10 10 I 10 I 10 10 10 I 10 ) 10 I log( 3 . 7 ) 10 I log( 10 dB 73 10 I ; I I log 10------- = = = = = = = = Another rule of thumb we get from this is that a 3dB change means a factor of 2 change in intensity. (73dB is twice the intensity of 70dB) similar to 12.70 A babys mouth is 30.0 cm from her fathers ear and 3.0m from her mothers ear. What is the difference of the sound intensity levels (in dB) heard by the father and by the mother? Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB similar to 12.70 A babys mouth is 30.0 cm from her fathers ear and 3.0m from her mothers ear. What is the difference of the sound intensity levels (in dB) heard by the father and by the mother? The first step is to find the ratio of the distances. Just divide them to find that the mother is 10 times farther away. Dont forget to look at the units 3.0m is 300cm. Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB similar to 12.70 A babys mouth is 30.0 cm from her fathers ear and 3.0m from her mothers ear. What is the difference of the sound intensity levels (in dB) heard by the father and by the mother? The first step is to find the ratio of the distances. Just divide them to find that the mother is 10 times farther away. Dont forget to look at the units 3.0m is 300cm. Now we can use this to find out what happens to the intensity when we compare the father and mother. Since sound intensity depends on 1/r 2 , the mothers intensity is 1/100 times the fathers intensity....
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12.2 Physics 6B Decibels and Doppler Effect - Physics 6B...

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