किसी द्रव से भरे बेलन (cylinder) में उसके पिस्टन को आगे-पीछे चलाकर किस प्रकार की तरंगें उत्पन्न की जाती हैं?

When a transverse wave strikes normally against a rigid wall and gets reflected, then:

The fundamental frequency of a closed organ pipe is equal to the frequency of the first overtone of an open organ pipe of length 60 cm. The length (in cm) of the closed organ pipe is: