Region: visible — green
- Wavelength
- 500 nm
- Frequency
- 5.9958 × 10¹⁴ Hz
- Energy per photon
- 3.9729 × 10⁻¹⁹ J
- In eV
- 2.4797 eV
- Per mole of photons
- 239.25 kJ/mol
- Wavenumber
- 20,000 cm⁻¹
c = λν and E = hν = hc/λ, with h = 6.62607015 × 10⁻³⁴ J s and c = 2.99792458 × 10⁸ m/s (exact SI values).
How it works
Light obeys c = λν, and each photon carries energy E = hν = hc ÷ λ. The calculator uses the exact SI values of the Planck constant, the speed of light and the elementary charge, and also gives the energy per mole of photons (multiply by the Avogadro constant) and the wavenumber in cm⁻¹ used in infrared spectroscopy.
For hydrogen, 1/λ = R_H (1/n₁² − 1/n₂²). Transitions ending on n = 1 form the ultraviolet Lyman series, n = 2 the visible Balmer series, and n = 3 the infrared Paschen series.
Frequently asked questions
- What is the energy of a 500 nm photon?
- E = hc/λ = (6.626 × 10⁻³⁴ × 2.998 × 10⁸) ÷ (500 × 10⁻⁹) = 3.97 × 10⁻¹⁹ J, or 2.48 eV, or 239 kJ per mole of photons.
- Why is the Balmer series visible?
- Transitions down to n = 2 release energies between about 1.9 and 3.4 eV, which fall in the visible range (656 nm red to 365 nm near-UV).
- How do I convert wavelength to frequency?
- Divide the speed of light by the wavelength in metres: ν = c ÷ λ.
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