During normal conversation sound heard at a 1meter distance is
**Core Concept**
The question is testing the concept of the intensity of sound perception in relation to distance. In normal conversation, the intensity of sound is within the range of 20-60 decibels (dB). The sound intensity decreases with increasing distance from the source, following the inverse square law.
**Why the Correct Answer is Right**
The correct answer is based on the fact that the human ear can detect sounds with intensities up to 120 dB, but sound levels above 85 dB can cause hearing damage. In a normal conversation, the speaker's voice is around 60-80 dB, which is within the safe range. At a distance of 1 meter, the sound intensity decreases, but it is still within the range that can be perceived by the human ear. This is because the sound waves are not yet attenuated to the point where they become inaudible.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** There is no specific distance at which sound becomes completely inaudible in a normal conversation. The perception of sound intensity varies from person to person and depends on various factors, including the speaker's voice, background noise, and the listener's hearing threshold.
* **Option C:** This option is not provided.
* **Option D:** This option is not provided.
**Clinical Pearl / High-Yield Fact**
In medical practice, it's essential to consider the impact of noise exposure on patients' hearing. Prolonged exposure to loud sounds can cause permanent hearing damage, so it's crucial to use hearing protection in high-risk environments, such as construction sites or music venues.
**Correct Answer: A. 60 decibels.**