12.1 Characteristics of Sound Range of human hearing ~ 20 – 20,000 Hz Infrasonic (< 20 Hz) Earthquakes, nuclear test detection, machines Ultrasonic (> 20,000 Hz) Medicine (fetal development, tumor removal, etc.), camera ranger, jewelry cleaning, animal sonar/echolocation 4/21/2017 APHY201

12.1 Characteristics of Sound The speed of sound in a material depends on the material’s elastic and inertial properties and its temperature. 4/21/2017 APHY201

12.1 Characteristics of Sound When the pressure is high, the displacement is low. 4/21/2017 APHY201

12.2 Intensity of Sound For humans: threshold of hearing (I ~ 10-12 W/m2) and pain (I ~ 1 W/m2) We perceive differences in loudness as logarithmic For humans: threshold of hearing (β = 0 dB) and pain (β = 120 dB) 4/21/2017 APHY201

12.4 Sources of Sound The harmonics are determined by whether the column is open at both ends or closed at one end. 4/21/2017 APHY201

12.5 Quality of Sound 4/21/2017 APHY201

12.6 Interference of Sound Waves The speakers emit at same frequency and are in phase The waves at C constructively interfere (path difference = nλ) and at D destructively interfere (path difference = {n+½} λ) What do you hear if the speakers emit different frequencies? 4/21/2017 APHY201

12.7 Doppler Effect Apparent change in frequency due to the motion of the sound source and/or the observer. 4/21/2017 APHY201

In class: Other problems ↓ 13. (a) From Table 12-2, the intensity in normal conversation, when about 50 cm from the speaker, is about 3x10-6 W/m2. (b) The number of people needed to produce 100 W of sound is 4/21/2017 APHY201

49. (a) Observer moving towards stationary source. (b) Observer moving away from stationary source. 4/21/2017 APHY201