Question

A person speaking normally produces a sound Intensity of 40 dB at a distance of 1m. If the threshold Intensity for reasonable audibility is 20 dB, the maximum distance at which he can be heard clearly is:

• A. 4m
• B. 5m
• C. 10m
• D. 20m

Answer 1

The correct option is C

10m

$40=10lo{g}_{10}\left(\frac{\frac{P}{4\pi (1{)}^2}}{I_0}\right)\dots \left(i\right)$

P – Power of sound energy of person

$20=10lo{g}_{10}\left(\frac{\frac{P}{4\pi x^2}}{I_0}\right)\dots \left(ii\right)$

(i) and (ii) gives 20 = $10lo{g}_{10}{x}^2$

$x=10m$