Harmonic help please

[V4viet]

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Sorry guys I know I'm suppose to post this in the MCAT questions thread..but no one is replying to me on there..so sorry for bothering you guys but I can't figure how to solve this problem..can someone please help me

A vibrating string has consecutive harmonics at wavelengths of 2 m and 4 m. What is the length of the string?

A. 1 m
B. 2 m
C. 4 m
D. 8 m

The answer is B..
I really don't understand what consecutive harmonics mean and how to go about solving this problem..can someone please help me?

 

[Shrike]

I missed something -- "no one's responding over there"? Your posts were five minutes apart in the two forums. (If you had posted it earlier, I missed it, sorry.)

Look to the sub-forum for a response, which I've now posted there. And maybe be a bit more patient.

 

[MeCord3]

Sorry guys I know I'm suppose to post this in the MCAT questions thread..but no one is replying to me on there..so sorry for bothering you guys but I can't figure how to solve this problem..can someone please help me

A vibrating string has consecutive harmonics at wavelengths of 2 m and 4 m. What is the length of the string?

A. 1 m
B. 2 m
C. 4 m
D. 8 m

The answer is B..
I really don't understand what consecutive harmonics mean and how to go about solving this problem..can someone please help me?

The length of a string is equal to (wavelength)👎/2, where n is the harmonic. You're told that you have consecutive harmonics at wavelengths of 2 and 4. You need 2 consecutive harmonics that will each give you the same length for the string, those are the 2nd and 1st harmonics respectively for wavelengths of 2 and 4 m. Plugging those into the equation, you end up with a string length of 2 m.

L = (wl)👎/2
L = (4)(1)/2 = 2, this is the case where you're at n = 1 and wl = 4
L = (2)(2)/2 = 2, this is the case where you're at n = 2 and wl = 2

Hope this helps.

 

[HippocratesX]

Viet...if you want a more intuitive understanding of harmonics, take a look at a NOVA physics book under the waves section. It really explains it well using a guitar string as an example. That way, the equations make more sense too.