Table 12.2 lists 120 dB as the intensity level at the threshold of pain for humans. 

(a) Show that the corresponding pressure amplitude is 29 Pa. 

(b) What is this pressure amplitude as a fraction of atmospheric pressure?

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Table 12.2 Pressure Amplitudes, Intensities, and Intensity Levels of a Wide Range of Sounds in Air at 20°C (Room Temperature) Pressure Amplitude Amplitude Intensity (Pa) Pressure Intensity Level (dB) Sound (atm) (W/m?) Threshold of hearing 3ж 10-10 3х 10-5 10-12 Leaves rustling 1x 10-9 1x 10-4 10-11 10 Whisper (1 m away) 3 x 10-9 3 x 10-4 10-10 20 Library background 1x 10-8 0.001 10-9 30 noise 3 x 10-8 Living room background noise 0.003 10-8 40 Office or classroom 1x 10-7 0.01 10-7 50 Normal conversation 3 x 10-7 0.03 10-6 60 at 1m Inside a moving car, 1x 10-6 0.1 10-5 70 light traffic 10-4 City street (heavy traffic) 3 x 10-6 0.3 80 1 x 10-5 10-3 90 Shout (at 1 m); or inside a subway train; risk of hearing damage if exposure lasts several hours Car without muffler at 3х 10-5 10-2 100 1m Construction site 1x 10-4 10 10-1 110 Indoor rock concert; 3 x 10-4 30 120 threshold of pain; hearing damage occurs rapidly Jet engine at 30 m 1x 10-3 100 10 130 3.