Loudness of sound from an isotropic point source at a distace of `70cm` is `20dB`. What is the distance (in m) at which it is not heard.

Explanation

To solve the problem step by step, we will follow the reasoning provided in the video transcript.

### Step 1: Understand the relationship between loudness (β) and intensity (I)
The loudness in decibels (β) is given by the formula:
\[ \beta = 10 \log \left(\frac{I}{I_0}\right) \]
where \(I_0 = 10^{-12} \, \text{W/m}^2\) is the reference intensity.
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