Final answer:
Waves A (4 MHz), B (400 kHz), and D (2 Hz) are inaudible to humans, while C (28 Hz) might be audible but is close to the lower limit of human hearing. The human hearing range is typically from 20 Hz to 20,000 Hz.
Step-by-step explanation:
To identify all the waves that are inaudible to the human ear, we need to understand the range of frequencies that humans can typically hear. The normal range of human hearing is from about 20 Hz to 20,000 Hz. Any sound outside of this range is considered inaudible.
- 4 MHz (4,000,000 Hz) is well above the highest frequency of human hearing and is used in applications like medical ultrasound.
- 400 kHz (400,000 Hz) is also above the range of human hearing and can be used in industrial, scientific, and medical applications.
- 28 Hz is within the lower limits of human hearing, although it would be very faint and some individuals might not perceive it.
- 2 Hz is below the threshold of human hearing and cannot be heard at all.
Therefore, waves A (4 MHz), B (400 kHz), and D (2 Hz) are inaudible to humans, while C (28 Hz) could be audible or inaudible depending on the individual's hearing ability and the intensity of the sound.