In
analogy to waves travelling on a string, particle waves too
can lead to standing waves under resonant conditions From
Chapter 14 of Class XI Physics  textbook, we know that when
a string is plucked, a vast number of wavelengths are excited 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