Sound Intensity and Sound Level Quiz

PDF page 437: In a quiet forest, you can sometimes hear a single leaf fall to the ground. But in a traffic jam filled with honking cars, you may have to shout just so the person next to you can hear Figure 14.9.The loudness of a sound is related to how energetically its source is vibrating. In cartoons showing a screaming person, the cartoonist often shows an open mouth with a vibrating uvula (the hanging tissue at the back of the mouth) to represent a loud sound coming from the throat. Figure 14.10 shows such a cartoon depiction of a bird loudly expressing its opinion. A useful quantity for describing the loudness of sounds is called sound intensity. In general, the intensity of a wave is the power per unit area carried by the wave. Power is the rate at which energy is transferred by the wave. In equation form, intensity I is

PDF page 443: c. Intensity is the power per unit area carried by a wave.

PDF page 437: where P is the power through an area A. The SI unit for I is W/m . The intensity of a sound depends upon its pressure amplitude.

PDF page 437: In a quiet forest, you can sometimes hear a single leaf fall to the ground. But in a traffic jam filled with honking cars, you may have to shout just so the person next to you can hear Figure 14.9.The loudness of a sound is related to how energetically its source is vibrating. In cartoons showing a screaming person, the cartoonist often shows an open mouth with a vibrating uvula (the hanging tissue at the back of the mouth) to represent a loud sound coming from the throat. Figure 14.10 shows such a cartoon depiction of a bird loudly expressing its opinion. A useful quantity for describing the loudness of sounds is called sound intensity. In general, the intensity of a wave is the power per unit area carried by the wave. Power is the rate at which energy is transferred by the wave. In equation form, intensity I is

PDF page 443: a. Power is the rate at which energy is transferred by a sound wave.

PDF page 438: medium, in units of m/s. Pressure amplitude has units of pascals (Pa) or N/m . Note that Δp is half the difference between the maximum and minimum pressure in the sound wave. We can see from the equation that the intensity of a sound is proportional to its amplitude squared. The pressure variation is

PDF page 438: proportional to the amplitude of the oscillation, and so I varies as (Δp) . This relationship is consistent with the fact that the sound wave is produced by some vibration; the greater its pressure amplitude, the more the air is compressed during the vibration. Because the power of a sound wave is the rate at which energy is transferred, the energy of a sound wave is also proportional to its amplitude squared.

PDF page 438: proportional to the amplitude of the oscillation, and so I varies as (Δp) . This relationship is consistent with the fact that the sound wave is produced by some vibration; the greater its pressure amplitude, the more the air is compressed during the vibration. Because the power of a sound wave is the rate at which energy is transferred, the energy of a sound wave is also proportional to its amplitude squared.

PDF page 438: an intensity of 10 W/m is β = 0 dB, because log10 1 = 0. That is, the threshold of human hearing is 0 decibels. Each factor of 10 in intensity corresponds to 10 dB. For example, a 90 dB sound compared with a 60 dB sound is 30 dB greater, or

PDF page 438: an intensity of 10 W/m is β = 0 dB, because log10 1 = 0. That is, the threshold of human hearing is 0 decibels. Each factor of 10 in intensity corresponds to 10 dB. For example, a 90 dB sound compared with a 60 dB sound is 30 dB greater, or

PDF page 438: an intensity of 10 W/m is β = 0 dB, because log10 1 = 0. That is, the threshold of human hearing is 0 decibels. Each factor of 10 in intensity corresponds to 10 dB. For example, a 90 dB sound compared with a 60 dB sound is 30 dB greater, or

PDF page 438: three factors of 10 (that is, 10 times) as intense. Another example is that if one sound is 10 as intense as another, it is 70 dB higher. Since β is defined in terms of a ratio, it is unit-less. The unit called decibel (dB) is used to indicate that this ratio is multiplied by

PDF page 440: Show that if one sound is twice as intense as another, it has a sound level about 3 dB higher. STRATEGY You are given that the ratio of two intensities is 2 to 1, and are then asked to find the difference in their sound levels in decibels. You can solve this problem using of the properties of logarithms. Solution

PDF page 440: Therefore, Discussion This means that the two sound intensity levels differ by 3.01 dB, or about 3 dB, as advertised. Note that because only the ratio I2/I1 is given (and not the actual intensities), this result is true for any intensities that differ by a factor of two. For example, a 56.0 dB sound is twice as intense as a 53.0 dB sound, a 97.0 dB sound is half as intense as a 100 dB sound, and so on.

PDF page 440: Discussion This 87.0 dB sound has an intensity five times as great as an 80 dB sound. So a factor of five in intensity corresponds to a difference of 7 dB in sound intensity level. This value is true for any intensities differing by a factor of five.

PDF page 438: three factors of 10 (that is, 10 times) as intense. Another example is that if one sound is 10 as intense as another, it is 70 dB higher. Since β is defined in terms of a ratio, it is unit-less. The unit called decibel (dB) is used to indicate that this ratio is multiplied by

PDF page 437: where P is the power through an area A. The SI unit for I is W/m . The intensity of a sound depends upon its pressure amplitude.