Final answer:
The conversion of sound intensity and frequency to phons requires reference to equal-loudness contours, which are not provided. Therefore, the phon level of a 0.0005 W/m^2, 40 Hz sound cannot be accurately determined without additional information.
Step-by-step explanation:
The student has asked about converting a sound with a given intensity and frequency into phons. Phons is a unit of loudness level for pure tones, referenced to the perceived loudness of a 1 kHz tone. To determine the phon level, one would need to use equal-loudness contours which are not provided in the question. However, it typically involves comparing the sound in question to a reference sound at 1 kHz which has a defined level in decibels.
Without additional information such as a reference equal-loudness contour chart or formula, we cannot assign an accurate phon value to the 0.0005 W/m^2, 40 Hz sound. The correct approach would involve using the reference at 1 kHz and adjusting the decibel level according to the equal-loudness contour for 40 Hz, and then converting that level into phons.