Final answer:
The wavelength of the standing wave produced when plucking a guitar string and hearing the fundamental harmonic is twice the length of the string (λ1 = 2L).
Step-by-step explanation:
When you pluck a guitar string and hear the sound that comes from the fundamental harmonic, this refers to the simplest standing wave that can exist on the string. In this scenario, the wavelength of the standing wave being produced is twice the length of the vibrating part of the string, which can be expressed as λ1 = 2L. The fundamental frequency is the lowest frequency of vibration, and when we look at a standing wave on a plucked string, this corresponds to a pattern with one antinode in the middle and nodes at the ends of the string. The wavelength of the fundamental harmonic in this case is therefore twice the length of the string.