Final answer:
The human hearing range is 20 Hz to 20,000 Hz. The minimum variation for distinguishing between two sounds is 1 Hz, and the beat frequency from two waves of 300 Hz and 340 Hz is 40 Hz.
Step-by-step explanation:
The range of frequencies that humans are capable of hearing is 20 Hz to 20,000 Hz, which corresponds to option (d). For humans to distinguish two separate sounds, the frequencies must vary by a minimum of 1 Hz, as per option (d) in the provided question. The beat frequency produced by the superposition of two waves with frequencies of 300 Hz and 340 Hz is 40 Hz (option d). Lastly, when discussing intensities of sound, the intensity levels in watts per meter squared vary by frequency but are also influenced by decibel levels. At a barely audible level, the intensity can be incredibly low, much less than 1 W/m2, for both 200 Hz and 4000 Hz sounds.