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.

29. Based on Figure 2, the attenuation coefficient for a 1,000 Hz sound wave in air at 20°C reaches a minimum value at a relative humidity closest to which of the following?

Answer and Explanation

Your Answer is

Correct Answer is B

Explanation

Looking at the description of Figure 2, you can also know that the experimental environment of Figure is 20 degrees. According to the requirements of the question, 1000Hz corresponds to the top line of Figure 2. Finding the minimum value of the vertical axis should correspond to the horizontal coordinate between 40-50, so the option B45% is within this range.