Photon energy

Physics Photon energy is directly proportional to frequency. E = hf where • E is energy (joules in the SI system) • h is the Planck constant • f is frequency where h is the Planck constant, c is the speed of light, and e is the elementary charge. The photon energy of near infrared radiation at 1 μm wavelength is approximately 1.2398 eV. == Examples ==

An FM radio station transmitting at 100 MHz emits photons with an energy of about . This minuscule amount of energy is approximately times the electron's mass (via mass–energy equivalence). Very-high-energy gamma rays have photon energies of 100 GeV to over 1 PeV (1011 to 1015 electronvolts) or 16 nJ to 160 μJ. This corresponds to frequencies of to . During photosynthesis, specific chlorophyll molecules absorb red-light photons at a wavelength of 700 nm in the photosystem I, corresponding to an energy of each photon of ≈ 2 eV ≈ ≈ 75 kBT, where kBT denotes the thermal energy. A minimum of 48 photons is needed for the synthesis of a single glucose molecule from CO2 and water (chemical potential difference ) with a maximal energy conversion efficiency of 35%. == See also ==