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Question:

The fundamental frequency of a closed organ pipe of length 20 cm is equal to the second overtone of an organ pipe open at both the ends. The length of organ pipe open at both the ends is :

140 cm

80 cm

120 cm

100 cm

Solution:

V/4Lclosed = 3V/2Lopen ⇒ 1/4×20 = 3/2Lopen ⇒ Lopen = 120cm