TPR Chapter 12: Sounds

The threshold of human hearing for loudness

10^-12 W/m^2

Speed of sound value

340 m/s

Decibel (dB) equation

A unit used to compare the loudness of different sounds. For every increase in the I by a factor of 10, add 10 to B. For every decrease in I by a factor of 10, subtract 10 from B.

Doppler effect

An observed change in the frequency of a wave when the source or observer is moving.

Beats

Changes in amplitude. Occurs when two waves with similar frequency interfere with each other.

Doppler effect equation

FD = Fs (V +/- Vd)/ (V -/+ Vs) where V = speed of sound in the medium Vd = speed of the detector Vs = speed of the source Top sign is towards. If detector is moving towards source, use "+" sign. If source is moving towards detector, use "-" sign.

Fifth harmonic of standing wave in a closed pipe.

Fifth harmonic for closed pipe has: - 5/4 of a wavelength. L = 5(1/4λ). λ = 4/5L. F = v/(4/5L).

First harmonic of standing wave in a closed pipe.

First harmonic for closed pipe has: - 1/4 of a wavelength. L = 1(1/4λ). λ = 4L F = v/4L

First harmonic (fundamental) of open pipe.

First harmonic for open pipe has: - 1 node. - 1/2 of a wavelength. L = 1(1/2 λ). λ = 2L. F = v/2L.

Intensity equation. Why do sound get softer?

I = P/A. Intensity is indirectly proportional to square of distance. Intensity is directly proportional to square of amplitude. As area increases, intensity decreases. Also attenuation: power is lost to the medium itself.

Redshift and Blueshift

Red: travelling away from earth, lower freq Blue:travelling towards earth, higher freq.

Second harmonic (fundamental) of open pipe.

Second harmonic for open pipe has: - 2 node. - A full wavelength. L = 2(1/2 λ). λ = L F = v/L.

- Speed of sound wave equation. - In what medium is the speed of sound the fastest? - When the speed of sound enters a new medium does it frequency change? does it speed change?

Speed (v) = √ bulk modulus/density. Depends on bulk modulus, density, temperature, pressure and humidity. Sound travels fastest in solid medium and slowest in gas medium. When a wave enter a new medium, its speed changes, but the frequency does not change.

Third harmonic of standing wave in a closed pipe.

Third harmonic for closed pipe has: - 3/4 of a wavelength. L = 3(1/4λ). λ = 4/3L. F = v/(4/3L).

Third harmonic (fundamental) of open pipe.

Third harmonic for open pipe has: - 3 node. - 1/2 of a wavelength. L = 3(1/2 λ). λ = 2/3L F = 3v/2L

Sound waves

Type of longitudinal wave, that can propagate in any medium: gas, solid and liquid. Speed of the sound waves depends on the medium's resistance to compression (bulk modulus) and the density. Not on the frequency or wavelength.

Longitudinal waves

Waves (such as a sound wave) in which the particles of the medium oscillates in the same direction as the wave.

What happens to the sound level, when the intensity: a. increases by a factor of 100? b. decreases by a factor of 90%? c. increases by a factor of 30?

a. increases by a factor of 100? I --> 100 I = 10 x 10 x 1. B--> B + 10 + 10 = B + 20 dB. b. decreases by a factor of 90%? I-90% = 0.1 I = I/10. B --> B - 10 dB. c. increases by a factor of 30? I increases by factor 30. 10 I < 30 I < 100 I B + 10 < B + 15 < B+20

parts of a longitudinal wave

compression, rarefaction, wavelength

Intensity

Intensity is power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy

Nodes and antinodes in closed pipe

Node: closed end of the pipe. Maximum pressure fluctuation. Antinode: open end of a pipe. Has constant pressure