Exposure to 90 db and 4000Hz noise results in –
**Core Concept**
Noise-induced hearing loss (NIHL) is a type of sensorineural hearing loss caused by prolonged exposure to loud sounds, particularly those above 85 decibels (dB). The damage occurs due to the mechanical stress and heat generated by the sound waves, leading to the degeneration of the hair cells in the cochlea.
**Why the Correct Answer is Right**
Prolonged exposure to 90 dB and 4000 Hz noise can cause significant damage to the hair cells in the cochlea, particularly those responsible for high-frequency hearing. This is because the energy density of sound waves increases with frequency, making high-frequency sounds more damaging at the same intensity. The 4000 Hz frequency is particularly susceptible to NIHL due to its high energy density and the limited protection offered by the middle ear. The damage to the hair cells leads to a permanent loss of hearing sensitivity, particularly in the affected frequency range.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it fails to specify the frequency and intensity of the noise, which are critical factors in determining the risk of NIHL.
**Option B:** This option is incorrect because it implies that NIHL is caused by a single exposure to loud noise, whereas the condition is typically the result of prolonged exposure over time.
**Option C:** This option is incorrect because it suggests that NIHL is limited to only one ear, whereas the condition can affect both ears equally.
**Clinical Pearl / High-Yield Fact**
The National Institute for Occupational Safety and Health (NIOSH) recommends that workers be protected from noise levels exceeding 85 dB, and that employers implement hearing conservation programs to prevent NIHL.
**Correct Answer: A. Prolonged exposure to 90 dB and 4000 Hz noise can cause significant damage to the hair cells in the cochlea, leading to noise-induced hearing loss.**