The air in a pipe, of length l and open at both ends, vibrates with a fundamental frequency f. What is the fundamental frequency of a pipe of length 1.5l and closed at one end?

A. \(\frac{f}{3}\)

B. \(\frac{2f}{3}\)

C. \(\frac{3f}{2}\)

D. 3f

A

Around the same number of candidates opted for A, B and C. The better candidates clearly favored the correct response, A. A quick and simple sketch reveals the answer immediately – this should be the candidates’ natural reaction given a resonance problem of this nature.