Intermediate Topic 40 of 1102 Atomic Structure & Periodicity
Photon
A quantum of light carrying energy E equals h times frequency.
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In-depth explanation of Photon
A photon is a quantum of electromagnetic radiation with zero rest mass, energy E = h nu = hc / lambda, and momentum p = h / lambda. Light shows wave behaviour in interference and diffraction and particle behaviour in absorption and in the photoelectric effect, a duality central to quantum theory. Photon energy depends only on frequency, not on intensity, so more photons of the same frequency carry more total energy. Photons are emitted when electrons fall to lower energy levels and absorbed when electrons are promoted to higher ones. Their energies are often given in electronvolts.
Going deeper: Photon
Key ideas: A photon is a quantum of light with energy E = h nu = h c / lambda and momentum p = h / lambda, no rest mass and no charge. Number of photons per second = power / photon energy. A 100 W lamp emitting 500 nm light radiates about 2.5 x 10^20 photons per second if all power is light.
Common mistakes and connections: Students think photons have mass because light is bent by gravity; they carry momentum and energy, but no rest mass. Another error is saying a photon of higher intensity has more energy; intensity means more photons, not larger photon energy. Photons are exchanged in absorption and emission transitions.
Visualization of Photon
Photon energy is inversely proportional to wavelength: ultraviolet photons carry over 3 eV, red photons only about 1.8 eV. The interactive lesson shows this as a live animation or chart.
Worked example and use case
A blue photon at 450 nm carries about 2.76 eV, since E = 1240 eV nm / 450 nm.
Frequently asked questions about Photon
What is Photon?
A quantum of light carrying energy E equals h times frequency.
Is Photon a beginner, intermediate or advanced topic?
Photon is a intermediate topic in Atomic Structure & Periodicity. It builds on the vocabulary of beginner topics in this area.
What should I learn before Photon?
Study these earlier topics in Atomic Structure & Periodicity first: Photoelectric Effect, Threshold Frequency, Work Function.
What comes after Photon?
The next topics in Atomic Structure & Periodicity are Atomic Emission Spectra and Atomic Absorption Spectra.
Can I practise Photon with quizzes?
Yes. The interactive lesson includes a self-check question on Photon, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Where Photon fits in Atomic Structure & Periodicity
Photon is topic 40 of 115 in Atomic Structure & Periodicity.