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Wave Speed - Section 12D


1. The speed of sound in sea water is about 1530 m/s. If a sound wave has a frequency of 2.50 x 102 Hz, what is its wavelength in sea water?


2. Cicadas produce a sound that has a frequency of 123 Hz. What is the wavelength of this sound in the air? The speed of sound in air is 334 m/s.


3. Human fingers are very sensitive, detecting vibrations with amplitudes as low as 2.0 x 10–5 m. Consider a sound wave with a wavelength exactly 1000 times greater than the lowest amplitude detectable by fingers. What is this wave’s frequency?


4. A nineteenth-century fisherman’s cottage in England is only 2.54 m long. Suppose a fisherman whistles inside the cottage, producing a note that has a wavelength that exactly matches the length of the house. What is the whistle’s frequency? The speed of sound in air is 334 m/s.


5. The lowest vocal note in the classical repertoire is low D (f =73.4 Hz), which occurs in an aria in Mozart’s opera Die Entführung aus dem Serail. If low D has a wavelength of 4.50 m, what is the speed of sound in air?

6. The highest-pitched sound that a human ear can detect is about 21 kHz. On the other hand, dolphins can hear ultrasound with frequencies up to 280 kHz. What is the speed of sound in water if the wavelength of ultra-sound with a frequency of 2.80 x 105 Hz is 0.510 cm? How long would it take this sound wave to travel to a dolphin 3.00 km away?