12.1 Characteristics of Sound Range of human hearing ~ 20 – 20,000 Hz Infrasonic (< 20 Hz)

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 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. APHY201

12.1 Characteristics of Sound • When the pressure is high, the displacement is low. 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) APHY201

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

12.5 Quality of Sound 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? APHY201

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

49. (a) Observer moving towards stationary source. (b) Observer moving away from stationary source. APHY201

12.1 Characteristics of Sound Range of human hearing ~ 20 – 20,000 Hz Infrasonic (< 20 Hz)