Option 1: Auditory nerve is not the part of the human ear that converts pressure variations associated with sound waves to electrical signals. The auditory nerve is responsible for transmitting these electrical signals from the cochlea to the brain for processing.

Option 2: Cochlea is the correct answer. The cochlea is a spiral-shaped structure in the inner ear that is responsible for converting the mechanical energy of sound waves into electrical signals that can be interpreted by the brain. Inside the cochlea, the hair cells detect the pressure variations of sound waves and convert them into electrical signals. These electrical signals are then transmitted through the auditory nerve to the brain for processing and interpretation.

Option 3: The eardrum, also known as the tympanic membrane, is not directly involved in converting pressure variations of sound waves into electrical signals. Instead, it acts as a barrier between the outer ear and the middle ear, vibrating in response to sound waves and transmitting these vibrations to the three small bones in the middle ear.

Option 4: The eustachian tube is not involved in converting pressure variations of sound waves into electrical signals. It serves to equalize the pressure between the middle ear and the air outside the body, helping to maintain proper functioning of the ear.

In conclusion, the