# What is the acoustic power of each pulse?

1. Sep 27, 2010

### rpullo

1. The problem statement, all variables and given/known data

In search for insects, a bat uses an echolocating system based on pulses of high frequency sound. These pulses are 2.0 ms in duration, have a frequency of 50 kHz, and have an intensity level of 100 dB at 1.0 m from the bat's mouth. Assume that the bat produces spherical acoustic waves.

a.What is the acoustic power of each pulse?
b. A bug is located 5.0 m from the bat. The effective cross-sectionl area of the insect is 10 mm2. How much of the acoustic power emitted by the bat is intercepted by the insect?

2. Relevant equations

I = P/A
E = Pt

3. The attempt at a solution

a. Given intensity level, I can find intensity...

10log(I/I0) = 100 [I0 = 10-12
I = 0.01

P = 0.01 x 4 x [pi] x 12 = 0.13 W

Textbook has 0.12, so I was wondering if I did it correctly.

b. I found the intensity of the pulse at 5 m to be 3.8 x 10-4 so...

P = AI = (0.001)(3.8 x 10-4) = 3.8 x 10-6

Textbook has it to power -10, so I'm wondering if someone can find a mistake..
Thanks!