Photon Energy (E = hf)
Also known as E = hf · planck relation
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Constant used — built into this formula, no need to enter
Planck constant · exactLearning zone
Planck introduced E = hf in 1900 as a desperate mathematical trick to fix blackbody radiation; Einstein took it literally in 1905 and light became grainy. Each photon carries an energy set only by its frequency — brightness just counts photons. With h = 6.626 × 10⁻³⁴ J·s, a green photon at 5.5 × 10¹⁴ Hz carries about 3.6 × 10⁻¹⁹ J, or 2.3 eV. That graininess is why ultraviolet burns skin while any amount of red light cannot: chemistry responds to the energy per photon, not the total delivered.
Photon Energy (E = hf)
Where
- = Photon energy
- = Frequency
Missing one of these? Work it out first, then come back
- Photon energy — Photon Energy from Wavelength (E = hc/λ), Photoelectric Effect
- Frequency — Wave Speed (v = fλ), Period-Frequency Relation