1. SPH3U

2. INTENSITY Waves transport energy

3. MEASURING ENERGY DEPOSITED ON A SURFACE AREA Unit: W/m 2 whisper10 -12 W/m 2 loudest1 W/m 2 pain10 W/m 2

4. Distance from source(m)Intensity (W/m 2 ) 1160 239 318 411 58 65 73 82.5 92.0 101.5

5. Determine the equation relating Intensity to Distance from the source. Intensity = ???

7. I  1/d n, n › 0 try n = 1 1/d (1/m)Intensity (W/m 2 ) 1160 0.539 0.3318 0.2511 0.208 0.175 0.143 0.132.5 0.112.0 0.101.5

9. try I α 1/d 2 1/d 2 (1/m 2 )Intensity (W/m 2 ) 1160.2539.1118.0611.048.035.023.0162.5.0122.0 0.011.5

11. I α 1/d 2 I = k(1/d 2 ) k = slope I = 159/d 2

12. Relationship between Intensity and distance from the Source Inverse square relationship I α 1/d 2

13. Decibel Scale STEP 1: the intensity of a sound (I 1 ) is compared to that of a whisper (I 0 ) STEP 2: take log 10 STEP 3: multiply by 10 I = 10 log 10 (I 1 /I 0 )

14. Intensity (W/m 2 )step 1: comparestep 2: take logintensity in dB I1I1 I 1 /I 0 log 10 (I 1 /I 0 )10log(I 1 /I 0 ) 10 -12 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 1 10

15. Intensity (W/m 2 )step 1: comparestep 2: take logintensity in dB I1I1 I 1 /I 0 log 10 (I 1 /I 0 )10log(I 1 /I 0 ) 10 -12 10 -12 /10 -12 = 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 1 10

16. Intensity (W/m 2 )step 1: comparestep 2: take logintensity in dB I1I1 I 1 /I 0 log 10 (I 1 /I 0 )10log(I 1 /I 0 ) 10 -12 10 -12 /10 -12 = 1 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 1 10

17. Intensity (W/m 2 )step 1: comparestep 2: take logintensity in dB I1I1 I 1 /I 0 log 10 (I 1 /I 0 )10log(I 1 /I 0 ) 10 -12 10 -12 /10 -12 = 1log 10 (1) = 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 1 10

18. Intensity (W/m 2 )step 1: comparestep 2: take logintensity in dB I1I1 I 1 /I 0 log 10 (I 1 /I 0 )10log(I 1 /I 0 ) 10 -12 10 -12 /10 -12 = 1log 10 (1) = 010(0) = 0 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 1 10

19. Intensity (W/m 2 )step 1: comparestep 2: take logintensity in dB I1I1 I 1 /I 0 log 10 (I 1 /I 0 )10log(I 1 /I 0 ) 10 -12 10 -12 /10 -12 = 1log 10 (1) = 010(0) = 0 10 -11 10 -11 /10 -12 = 10log 10 (10) = 110(1)=10 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 1 10

20. intensity I1I1 I 1 /I 0 log 10 (I 1 /I 0 )10log(I 1 /I 0 ) 10 -12 100 10 -11 101 10 -10 100 = 10 2 220 10 -9 1000 = 10 3 330 10 -8 10 4 440 10 -7 10 5 550 10 -6 10 6 660 10 -5 10 7 770 10 -4 10 8 880 10 -3 10 9 990 10 -210 10100 10 -1 10 11 11110 110 12 12120 1010 13 13130