Well, the power going out of the mouth is the same, what is changing is the area that power is spread over at some distance. Notice that area in a sphere (assuming the sound goes equally in all directions) changes by distance^2
dblevel= 10 log (P/Po)=10log(radiuso/radius)^2=20log (original distance/new distance)
So you want a 25 db increase (35 to 60)
25= 20 log (15/distance)
10^(25/20)= 15/distance
distance= 15/10^1.25=84 cm
check my thinking.
I am reposting this since I did so incorrectly the first time. (I apologize for posting it twice the first time as well...I accidently hit refresh) Here is the problem with the proper units:
You are trying to overhear a juicy conversation, but from your distance of 15.0m , it sounds like only an average whisper of 35.0 decibels . So you decide to move closer to give the conversation a sound level of 60.0 decibels instead. How close should you come? (in cm)
I Have no idea where to start with this problem....I don't even need an answer, but an equation to work with would be great. My college professor seemed to skip over decibels, but I'm having a hard time understanding it on my own. Thank you.
2 answers
the answer is C.