# Finding Frequency

1. Feb 12, 2008

### zachcumer

Hello,
I have to answer this question in my Physics Class. "What frequency of sound produces a wavelength of 1 meter in room-temperature air? "

Could you help me?

Thanks

2. Feb 12, 2008

### ranger

Can you tell us a formula that relates wavelength to its frequency?

Hint: it is an inverse relationship.

3. Feb 12, 2008

### zachcumer

In the book, they say Frequency=1/period...

4. Feb 12, 2008

### zachcumer

hello?

5. Feb 12, 2008

### ranger

Indeed, f = 1/T. But that doesn't really help you here since we need wavelength. Theres also a reason why they mentioned the medium to be air at room temperature. This should tell you that the velocity depends on the medium through which the wave propagates. Now that I've told you that wavelength is somehow related to velocity of the wave and its frequency, can you piece it together to get a formula?

It should be somehow be obvious that the higher the frequency, the smaller the wavelength.

6. Feb 12, 2008

### zachcumer

isnt the 1 meter the wavelength? confused????

7. Feb 12, 2008

### ranger

Yes. But I find it much easier to reason out a formula which gives us wavelength in terms of velocity and frequency. Then you can solve the equation for frequency (but thats just me). Just a side note, the speed that sound propagates in air is around 345 m/s at room temp.

8. Feb 12, 2008

### zachcumer

so its 345 times f= one meter....how do I find "f"?

9. Feb 12, 2008

### ranger

Nice try. But remember that wavelength is inversely proportional to frequency.

10. Feb 12, 2008

### zachcumer

oh its 344 thanks so so so so so so so much!

thanks again

11. Feb 12, 2008

### zachcumer

What is the shortest wavelength you can hear?

12. Feb 12, 2008

### ranger

Now that you have your formula relating frequency and wavelength. I'll tell you that the human ear has an audible range of about 20Hz - 20kHz. Its up to you express that as a wavelength.

13. Feb 12, 2008

### zachcumer

So, 345 times 20 equals 6,900 centimeters...!>...!.

14. Feb 12, 2008

### zachcumer

confused.

15. Feb 12, 2008

### ranger

16. Feb 12, 2008

### zachcumer

I know I have to do something similar on this problem too: A bat flying in a cave emits a sound and receives its echo 1 s later. How far away is the cave wall?

17. Feb 12, 2008

### ranger

The sound hits the wall in .5 secs and takes another .5 secs to return to the bat for a total time of 1 sec. What are the equations that relate velocity, time, and distance?

18. Feb 13, 2008

### zachcumer

so its 345/2 or half of the speed of sound....
thanks

19. Feb 13, 2008

Looks good.