This is measures by open harmonics frequency.
f= n*V/(4*1)
What is frequency?
Frequency refers to the number of waves that pass a fixed point in unit time. Frequency is denoted by the symbol f, and is measured in hertz (Hz).
Given,
f=220
velocity= 354 m/s
=> 220 = (nl)*(354)/(4*1)
=>1244 = (n2)*(354)/(4*1)
=> n2/n1= 5.65
=> n1=1, n2=6
=> = 40 cm (final answer).
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