Passage V

As a sound wave travels through a medium, the wave becomes attenuated (loses energy). The attenuation coefficient, α, is the rate at which the wave's intensity level (a measure of sound volume) decreases with distance as a result of this energy loss; the greater the value of α, the greater the decrease in intensity level with distance. Figure 1 shows, for waves of 3 different frequencies (in hertz, Hz), how α (in decibels per kilometer, dB/km) varies with temperature in air at 10% relative humidity.

Figure 2 shows, for waves of 3 different frequencies, how α varies with relative humidity in air at 20°C.

Figures adapted from Richard Lord, "Calculation of Absorption of Sound by the Atmosphere." ©2004 National Physical Laboratory.

28. What is the approximate maximum α shown in Figure 1 for a 200 Hz sound wave in air at 10% relative humidity, and at approximately what temperature does that maximum occur?

α (dB/km) ---- temperature (°C)

Answer and Explanation

Your Answer is

Correct Answer is F

Explanation

Look at the last sentence of the above description of Figure 1, clarify that the fixed environment of Figure 1 is 10% humidity, according to the requirements of the question, determine that the 200Hz line is the bottom line, and then match the options one by one, only when the abscissa is When -5, the vertical coordinate is 3km matching.