The second overtone of an open organ pipe has the same frequency as the first overtone of a closed pipe L metre long. The length of the open pipe will be

For second overtone (3rd harmonic) in open organ pipe,3λ2 = l0    ⇒ λ = 2l03For first overtone (3'd harmonic) in closed organ pipe,3λ4 = lC            ⇒ λ = 4lc3 = 4L3So,  2l03 = 4L3   ⇒l0 = 2L