Physics
posted by A, on .
A child has an ear canal that is 1.3cm long. At what sound frequencies in the audible range will the child have increased hearing sensitivity?

There will be enhanced sensitivity whenever the sound frequency corresponds to a fundamental or harmonic of an organ pipe with one open end and one closed end, 1.3 cm long. This will excite resonant oscillations within the ear

i appreciated your work... but how do i get answer in Hz.

There will be resonance whenever the 1.3 cm ear canal length equals an odd number of quarter wavelengths (1, 3, 5 etc.). For the fundamental resonant frequency, wavelength = 4x1.3 = 5.2 cm. Divide the sound speed (about 30,000 cm/s) by that wavelength for the frequency in Hz.
Check my thinking. I may have the fundamental resonant wavelength wrong. 
I didn't quite follow ...