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.

33. The graph below shows, for sound waves of 3 different frequencies, how α varies with relative humidity in air at a particular temperature.

Based on Figure 1, the particular air temperature is most likely which of the following?

Answer and Explanation

Your Answer is

Correct Answer is B

Explanation

The question stem requires information based on Figure 1, because the corresponding humidity in Figure 1 is 10%, so look at the picture given in question 33, and find that when the abscissa is 10, the ordinates are 3, 9, and 14 respectively; Look at Figure 1 again to find the abscissa when these three ordinates correspond to each other at the same time, only when it is 0 degrees.