Question

Humans can hear sounds with frequencies up to about 20.0 kHz, but dogs can hear frequencies up to about 40.0 kHz. Dog whistles are made to emit sounds that dogs can hear but humans cannot. If the part of a dog whistle that actually produces the high frequency is made of a tube open at both ends, what is the longest possible length for the tube? (Assume a temperature of 20° C.)

mm

I used this formula L = v/2*f1, I end up with 0.43 cm which should be 4.3mm but its wrong and I don't know why. Could someone please explain it to me. Thank you!

Answer 1

length is half wavelength.

frequency*2Length=velocity sound
length= (331+.6*20)/2*40E3

= 343/80E3=4.3mm

Answer 2

Thanks.Thats what I got too as my answer, but for some reason its wrong :/ I have no clue why.