# A closed-ended tube is 2.8 m long. What is the wavelength of a first harmonic standing wave?

So,we can say $l = \frac{\lambda}{4}$ where,$l$ is the length of the tube and $\lambda$ is the wavelength
So,for $1$ st harmonic $\lambda = 4 l = 4 \cdot 2.8 = 11.2 m$