# Sound wave reflection question

1. Nov 9, 2006

### Checkfate

Hello,

I am working on a problem, how would the echoes from a large and small insect compare if they were the same distance from a bat? (from the bats point of view of course)

I don't think they would differ at all. If the insects are not moving, then there would be no differance. The only way I could see a difference is if the insect were the shape of a parabola(lol).. Am I right?

Last edited: Nov 9, 2006
2. Nov 9, 2006

### Checkfate

After rethinking this question I think I am closer, but still don't have a definite answer.

The wavelength of the bat's sound will determine whether or not it can see the insect. Although the question uses words like "small and large" which are not very descriptive, I think they are suggesting they are at least big enough for the bat to see. Somewhere in my book it said a bat chirps at a frequency of 60KHz, so since sound travels at around 340m/s in the air, the bat can detect insects as small as 5.0mm roughly.

I think the main question here is how small is small? This question is starting to make me mad.

Given the information in the question, should there be a differance in the echo? I don't see how, I mean obviously it is going to have an effect but from 100feet away, the returning sound wave will be so spread out that I don't think it would be able to tell the differance. Perhaps it also depends on how far away the bat is... aghh

Last edited: Nov 9, 2006
3. Nov 9, 2006

### Checkfate

Okay, I think I finally found the answer I need, although I don't 100% understand it unfortunately, but I will be able to fix that with more studying. Thanks.

The solution I came across is that since small objects reflect less, the sound will be less intense when it gets to the bat. Or vice versa with the big insect the sound will be more intense. What I don't understand is why it will be more intense. It would make sense if the sound wave travelled straight and did not spread out at all, but this is not the case. Anyways, I'll figure it out, but if someone knows, I would appreciate an answer immensely. Thanks. :)