# How to find wavelenght of a 3m spring with 2,5 Hz?

1. Sep 8, 2014

### kontorstol

Hi! I just can't figure this out.

A 3m long spring makes transverse waves with a 2,5 Hz frequency. What is the wavelength?

I don't even know where to start, because in out incredible small physics course, we never learned this. :)

2. Sep 8, 2014

### valerioperi

Are these all the data you have? Does it say if the spring is fixed at its ends? Does it say if it's the fundamental armonic?

3. Sep 8, 2014

### kontorstol

Thats all the info. The only formula have have learned is λ = v/f, and that won't work here after what I can see. There are four options after the question:

a) 0.67m
b) 3.75m
c) 1.5m
d) 6m

4. Sep 8, 2014

### valerioperi

All right, then I think you have to assume that the spring is fixed at both its ends. Then you have a formula that states that only some particoular waves can occour in that spring (its armonics). Have you ever heard or seen this formula?

5. Sep 8, 2014

### BvU

Hello Konto, and welcome to PF. There must be more to this. Is there a preceding question that is continued in this one ?
If you can't find anything there, all I can advise is to look up (google) images of standing waves and see if you get some inspiration there....

6. Sep 8, 2014

### Domenico94

you should check out other data that they gave you. This way, it's just impossible to understand. :)

7. Sep 8, 2014

### kontorstol

First of all, sorry for not using the right template etc. when posting this topic. I will do better in future topics.

I have never heard about any other formula for finding wavelength than λ = v/f. We don't even have a book in physics, all the info we need is in a 75 page long compendium that the teacher made for the 6 week course, and the compendium never mentions such a formula.

This was the first question. :( I found a picture that was suppose to go with the question (didn't get printed). Maybe that can help?

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8. Sep 8, 2014

### valerioperi

Yes the picture is extremely useful because tell us that the spring is fixed at its end and the wave is its fourth armonic. There are a lot of beautiful videos that could help you understandig what we are talking about: try searching on YouTube stationary waves.
The formula anyway says that $$\lambda = \frac{2L}{n}$$ where L is the length of the spring and n the number of the armonic.
It's an interesting stuff, expecially if you are interested in music, so I suggest you to try to understand it on your own, or even better ask your teacher for some useful sources :)

9. Sep 8, 2014

### kontorstol

Well thats great news, thank you so much. :) Now I'll just have to ask the teacher why he would make a question that we never could figure out if we only look at the compendium. :)

10. Sep 8, 2014

### BvU

Looks as if you can now answer the question by just looking at the picture: how many wavelengths do you see ?

11. Sep 8, 2014

### kontorstol

Wow, I did not realize that. :) Thanks for opening my eyes. :)

12. Sep 8, 2014

### BvU

Just to be sure I didn't wrong-foot you: what is your conclusion?

13. Sep 8, 2014

### kontorstol

λ = 2*3m/4 = 1,5m :)

14. Sep 8, 2014

### BvU

Looks like the right answer to me !