(c) In case of closed organ pipe, fundamental frequency n
V
4L
=
332
4×83×10−2
or, n = 100 Hz Hence frequency of overtones n1:n2:n3 :------- = 1 : 3 : 3 i.e., 100,300,500,700 and900 Hz So number of possible natural oscillationsof air column whose frequencies lie below1000 are 5.