The de Broglie relations then showed that four-wavevector applied to matter waves as well as to light waves: P = ℏ ℏ K = ( E c , p → → ) = ℏ ℏ ( ω ω c , k → → ) . yielding E = ℏ ℏ ω ω and p → → = ℏ ℏ k → → , where ħ is the Planck constant divided by 2 π .