However only those wavelengths survive which have nodes
at the ends and form the standing wave in the string It means
that in a string, standing waves are formed when the total distance
travelled by a wave down the string and back is one wavelength, two
wavelengths, or any integral number of wavelengths Waves with other
wavelengths interfere with themselves upon reflection and their
amplitudes quickly drop to zero For an electron moving in nth circular
orbit of radius rn, the total distance is the circumference of the orbit,
2prn