KEAM 2018 Physics and Chemistry Paper

Given, v=320ms−1,l=1m
For an organ pipe whose one end is closed, only odd harmonics containing odd multiples of fundamental frequency are present.
Resonate frequency of first mode, n1=‌

v

4l

Second mode, n2=3n1
Third mode, n3=5n1
Fourth mode, n4=7n1
Fifth mode, n5=9n1
So, n1=‌

320

4

=80Hz
n2=3×80=240Hz
n3=5×80=400Hz
n4=7×80=560Hz
n5=9×80=720Hz
So according result, option (b) as multiple of cannot a resonating frequency of the pipe.