Planck/de Broglie relation

The Planck-Einstein relation states that for light, $E = h \nu$, or alternatively, $E = \hbar \omega$ where $\hbar = \frac{h}{2\pi}$.

The de Broglie relation extends this equation to apply to particles as well. The de Broglie wavelength of a particle is given by \lambda_\dB = \frac hp. From these two relations we find that $p = \frac h\lambda = \hbar k$.