The minimum frequency of the vibration is the fundamental frequency of the vibration. In a closed organ pipe, the fundamental frequency of vibration is given as,
ν = V/4L, where V = speed of the sound in air = 340 m/s and ν = 500 Hz. L = length of the pipe =? Thus, L =V/4ν =340/(4*500) m =340/2000 m
→L = 0.17 m = 17 cm.