Standing wave

1. Jul 5, 2008

pooka

A standing wave resonates at 400 Hz with three antinodes on a string tied tightly between two posts 2.0 meters apart.
What is the wavelength of this standing wave?
What is the fundamental frequency of this string?

I tried to draw the picture out, and it looks like the wavelength is just 2.0 m? I am not sure how to find the fundamental frequency though.

2. Jul 5, 2008

alphysicist

Hi pooka,

Before dealing with the fundamental frequency, I don't believe this wavelength is correct. If you look at it again, do you see what it is? Or if not, why did you choose 2m as the wavelength?

3. Jul 5, 2008

pooka

I chose this wavelength because when I drew the wave out, the post is 2 metres apart, so I thought that the wavelenght would also be 2 metres.

4. Jul 5, 2008

pooka

Okay I just redrew the wave. Is the wavelength 4/3 metres then?

5. Jul 5, 2008

alphysicist

That sounds right to me.

For your question in your original post, what is the definition of the fundamental frequency? Try drawing this string vibrating in its fundamental frequency (instead of the frequency they give you). Can you find its wavelength in that case? Does that help you find its frequency?

6. Jul 5, 2008

pooka

Is the fundamental frequency wavelength 4 m then?

7. Jul 5, 2008

alphysicist

Yes, that is the wavelength when it vibrates at its fundamental frequency.

8. Jul 5, 2008

thanks!

9. Jul 5, 2008

alphysicist

Sure, glad to help! (Just to be sure I understood the wording in one of your posts, you did use that 4m wavelength to find the fundamental frequency, right?)

10. Jul 5, 2008

pooka

Yup! The fundamental frequency is given by fn = v/λn.
I first found v by using the v = fλ where f is the 400 Hz times the wavelength 4/3

Then I divided the v by 4.

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