The wave function (in S.I. units) for an electromagnetic wave is given as:

$\Psi(x, t)=10^3 \sin \pi\left(3 \times 10^6 x-9-10^{14} t\right)$

In the above, wavelength of the wave is:

666 nm

$\Psi(x, t)=10^3 \sin 3 \times 10^6 \pi\left(x-3 \times 10^8 t\right)$

Comparing it with

$\Psi(\mathrm{x}, \mathrm{t})=\mathrm{a} \sin \frac{2 \pi}{\lambda}(\mathrm{x}-\mathrm{vt})$

∴ $\frac{2 \pi}{\lambda}=3 \times 10^6 \pi$

or $\lambda=\frac{2 \times 10^9}{3 \times 10^6}$ = 666 nm