# Sound wave in tube

## Homework Statement

"A sound wave of 40.0 cm wavelength enters the tube shown below at the source end. What must be the smallest radius r such that a minimum will be heard at the detector end?" (figure attached)

## Homework Equations

v =$$\lambda$$$$f$$

## The Attempt at a Solution

I don't have any idea how to do this problem. My first idea was to use the formula for the wavelength of a closed or open tube, but whether the tube is closed or open isn't given so I'm guessing that's not right. Also, I don't see how the radius of the half circle has anything to do with the tube through which the sound is traveling.

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