The velocity of a wave is calculated by v = λf. From this equation we can take the frequency f = v / λ and substitute in the energy equation to find a new equation for the calculation of the energy from the wavelength:
E = hc / λ
To calculate the photon energy, in eV (Electrovolt), when we have the value of the wavelength λ (necessarily given in Å - angstrom), we use an alternative equation given by:
[tex]E = \frac{12400}{\lambda} [/tex]
Data: 670.8 Å
Solving:
[tex]E = \frac{12400}{\lambda} [/tex]
[tex]E = \frac{12400}{670.8} [/tex]
[tex]\boxed{E \approx 18,4eV}[/tex]
