Standing waves on a string

A string $0.8\ \text{m}$ long, fixed at both ends, carries waves at $280\ \text{m/s}$, and has a mass of $0.005\ \text{kg}$ for each metre. You will make the program find its first four harmonics, the wavelength of the third, and the tension the string must have. Then it draws the first three standing waves.

The idea. $f_n = \dfrac{nv}{2L}$ and $\lambda_n = \dfrac{2L}{n}$. On a string $v = \sqrt{\dfrac{T}{\mu}}$, so $T = v^2\mu$.

Your tasks.

1. Inside the loop, work out f, the frequency of harmonic n.
2. Find lam3, the wavelength of the third harmonic, in metres.
3. Find T, the tension, in newtons.