58) We know that the guitar string creates a wave of wavelength λ and fundamental frequency f[1]. Now we want to find the wavelength when the guitar produces a wave of second harmonic. We can imagine this as a wave traveling through a tube open at both ends. We can use this equation to relate the two frequencies.
Using this equation we can tell that the second harmonic (n = 2) will have a frequency of 2 * f[1]. Now we can use our wave equation for velocity to solve for the wavelength.
It is important to note that we can equate the two blue equations because the velocity of the wave in both situations will be the same because the medium is the same for both situations.
Answer: A
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