Final answer:
The sound level at 20m from the source, where the original sound level at 10m is 20dB, would be approximately 10dB to 11dB, considering the inverse square law of sound intensity.
Step-by-step explanation:
If the sound level at a point 10m from the point source is 20dB, to find the sound level at a distance of 20m, we need to understand how sound intensity and distance are related. Sound intensity decreases with the square of the distance from the source, known as the inverse square law.
Using this law, if you double the distance from the source, the area over which the sound energy spreads is four times greater, and thus the intensity is one-fourth. Since each factor of 10 in intensity corresponds to a decrease of 10dB in the sound level, a decrease by a factor of 4 (which is close to 10) will result in a decrease in the sound level by slightly less than 10dB (because 10^0.6 is approximately 4). Therefore, if the sound level at 10m is 20dB, the sound level at 20m would be slightly more than 10dB lower, so approximately 10dB to 11dB.