Physics 1307 Quiz 6 Solution =I I= P A I dB =10log I A =4 r2 1/1
Physics 1307 Quiz 6 Solution At a recent rock concert, a dB meter registered 130 dB when placed 2.5 m in front of a loudspeaker on the stage. What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?
In order to find the power output we need first to find the intensity in W/m²: 130 =10 log 13= log
I −12
10
W / m2
I − 12
10
W / m2
10 13×10−12 W / m2 =10 W / m2 = I Now, we can relate the intensity with the power output assuming an isotropic emission: 2
I =10 W / m =
P 2
4 r 2 10 W / m ×4××2.5 m2 =785W =P
Useful equations:
I= I dB =10 log
P A
I 10
−12
W /m2
Asphere =4 r 2
1/1
In order to find the power output we need first to find the intensity in W/m²: 130 =10 log 13= log
I −12
10
W / m2
I − 12
10
W / m2
10 13×10−12 W / m2 =10 W / m2 = I Now, we can relate the intensity with the power output assuming an isotropic emission: 2
I =10 W / m =
P 2
4 r 2 10 W / m ×4××2.5 m2 =785W =P
Useful equations:
I= I dB =10 log
P A
I 10
−12
W /m2
Asphere =4 r 2
1/1
