Saturday, February 13, 2016

Speed of waves: Water

Question:
The bulk modulus of water is 2.04$\times$10$^9$ Pa. The frequency of a water wave is found to be 262 Hz. What is the wavelength?

Answer:
The density of water is 1000 kg/m$^3$. The speed of the wave is given by
\[
v = \sqrt{\frac{B}{\rho}}
\]
where $B$ and $\rho$ are the bulk modulus and the density, respectively. Plug in the numbers.
\[
v =  \sqrt{\frac{2.04\times 10^9}{1000}}=1428 \ \mathrm{m/s}
\]
We know the relationship:
\[
v = f\lambda
\]
Therefore, the wavelength is
\[
\lambda = \frac{v}{f}=\frac{1428}{262}=5.45 \ \mathrm{m}
\]

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