P105 Homework Assignment #5 | Complete Solution

Physics P105: Basic Physics of Sound
Homework Assignment #5:
Make sure you show your work online where relevant.

1. Standing waves have regions of minimum amplitude called nodes/antinodes and regions of maximum amplitude called nodes/antinodes .
2. The ________________ scale is a logarithmic scale used for comparing sound levels.
3. An open organ pipe (both ends open), 16 feet long, is operating in air at 20°C. The
fundamental frequency f1 = __________ Hz and the second harmonic frequency f2 = __________ Hz (1 ft = 0.3048 m).
4. Suppose the air is replaced by helium at 20°C (v = 1005 m/s). For an open pipe (both ends open), 16-ft in length, the new fundamental frequency f1 = __________ Hz.
5. In order to produce a fundamental frequency of 10 Hz in a stopped organ pipe (one end closed), the required length L = __________ m.
6. Two identical organ pipes, both at 20°C, have frequencies of 500 Hz. If the temperature of one pipeis raised to 33°C, its new frequency = __________ Hz.
7. One model of the outer ear canal is a cylindrical pipe 3.0 cm long that is closed at one end by the eardrum. The resonant (fundamental) frequency for this closed pipe is f1 = _____________ Hz.
8. Find the following logarithms: log 2 = ____________, log 4 = ____________, log 200 = ____________. (over)
9. Given log x, find the number x: log x = 0.3, x = ____________; log x = 3.00, x = ____________.
10. A sound of intensity I = 2.0 × 10-6 W/m2 falls on a detector of area A = 7 × 10-5 m2. (Note: this is about the size of an eardrum.) The total power P being received by this detector = ___________ W.
11. For a sound of intensity I = 2.0 × 10-6 W/m2, the sound intensity level (in decibels) Li = dB.
12. Given a sound with Lp = 50 dB, the sound pressure = ______________ N/m2 and the sound intensity = ______________ W/m2.
13. If two sounds differ in level by 46 dB, the ratio of their intensities = ______________.
14. If two sound sources independently cause sound intensity levels of 53 dB and 56 dB at a certain point, what is the total sound intensity level at that point when both sources contribute at the same time? LI = ______________ dB.
15. At a rock concert, a dB meter registers 125 dB when placed 3.0 m in front of a loudspeaker on the stage. [You may assume uniform spherical spreading of the sound from the speaker.] The sound power output of the speaker = ______________ W.
16. For a speaker whose sound power output is 140 dB, the distance from the speaker at which
the sound level will be reduced to 90 dB is ____________ m.