A steel tube, which is closed at both ends, is filled with air. If the next harmonic frequency is 60 Hz, what is the fundamental frequency?

Answer 1

Since the tube is closed at both ends then L=nλ/2 and v=fλ where λ=2L/n and f= v/λ so f=nv/2l or f_n = nv/2L. since f₂ =60Hz = 2v/2l =2(v/2l) v/2L= 30Hz and the fundamental frequency f₁ = v/2L then f₁ = 30Hz.