[填空题]
A dramatic demonstration, called “sin1:(jiagv pn(7bxvy ;e fjv*bzoq2 :t) ging rods,” involves a long, slender alumrot b 51c/jk4e y)*pvkinum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, lo 4p1)yek5 rjb/v t*okcud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound? $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod, m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C? m
