Page 203 - Schaum's Outline of Theory and Problems of Applied Physics

188 WAVES AND SOUND [CHAP. 15

15.10. An 80-dB sound relative to a 30-dB sound is more intense by a factor of
(a) 5 (c) 500
(b) 50 (d) 10 5

15.11. A sound intensity level of 55 dB is produced by 10 flutes. The number of flutes needed to produce a level of 65 dB
under the same circumstances is
(a) 20 (c) 100
(b) 60 (d) 200

Supplementary Problems

15.1. What quantity is carried by all types of waves from their source to the place where they are eventually absorbed?

15.2. Find the wavelength in air of a sound wave whose frequency is 440 Hz.

15.3. A tuning fork vibrating at 600 Hz is immersed in a tank of water, and the resulting sound waves in the water are
found to have a wavelength of 2.5 m. What is the velocity of sound in the water?

15.4. A wave of frequency f 1 and wavelength λ 1 goes from a medium in which its velocity is v to another medium in
which its velocity is 2v. Find the frequency and wavelength of the wave in the second medium.

15.5. A violin string is vibrating at a frequency of 440 Hz. How many vibrations does the string make while its sound
travels 200 m in air?

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15.6. What is the intensity in W/m of the 120-dB sound from a siren?
15.7. How many times more intense than the 60-dB sound of a person talking loudly is the 100-dB sound of a power lawn
mower?
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15.8. Soundwaveswhoseintensitiesexceedabout1W/m causedamagetotheear.Howmanydecibelsisthisequivalentto?

15.9. A certain jet aircraft produces sound of 140-dB intensity at a distance of 30 m. How many km away is the intensity
90 dB?

15.10. What is the power gain in decibels of an amplifier whose power input is 0.15 W and whose power output is 6 W?
15.11. Two pneumatic hammers are being used to dig up a pavement. If one of them produces a sound intensity level of
95 dB, what is the total sound intensity level?
15.12. What is the ratio between the output and input powers of a 30-dB amplifier?

15.13. A 60-dB amplifier has an output of 25 W. What is the input power?

15.14. A 1.2-kW radio transmitter is coupled to an antenna by a cable whose attenuation is 1.8 dB. How much power
reaches the antenna?

15.15. A preamplifier whose gain is 20 dB is used with a 50-dB amplifier. What is the total gain of the system?

15.16. The frequency of a train’s whistle is 800 Hz. The train is moving south at 120 km/h, and on a parallel road a car is
moving north toward the train at 80 km/h. What frequency is heard by the people in the car?