Photon Energy
Light consists of photons — discrete packets of energy. A photon's energy depends on its frequency: higher frequency (shorter wavelength) = more energy per photon.
Planck's Equations
E = h × f
E = h × c / λ
h = 6.626×10⁻³⁴ J·s (Planck's constant)
c = 3×10⁸ m/s (speed of light)
f = frequency (Hz)
λ = wavelength (m)Worked Examples
Green light (λ=550 nm = 5.5×10⁻⁷ m):
E = 6.626×10⁻³⁴ × 3×10⁸ / 5.5×10⁻⁷
E = 3.61×10⁻¹⁹ J = 2.26 eV
X-ray (λ=0.1 nm = 10⁻¹⁰ m):
E = 1.99×10⁻¹⁵ J = 12,400 eV = 12.4 keVJoules to Electron-Volts
1 eV = 1.602×10⁻¹⁹ J
E (eV) = E (J) / 1.602×10⁻¹⁹
Visible light: 1.7 eV (red) to 3.3 eV (violet)
UV photon: 3.4–124 eV
Gamma ray: >100 keVCalculate photon energy: Free Photon Energy Calculator