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  2. Speed of light - Wikipedia

    en.wikipedia.org/wiki/Speed_of_Light

    By adopting Einstein synchronization for the clocks, the one-way speed of light becomes equal to the two-way speed of light by definition. [20] [21] The special theory of relativity explores the consequences of this invariance of c with the assumption that the laws of physics are the same in all inertial frames of reference.

  3. Absorption cross section - Wikipedia

    en.wikipedia.org/wiki/Absorption_cross_section

    More generally, the term cross-section is used in physics to quantify the probability of a certain particle-particle interaction, e.g., scattering, electromagnetic absorption, etc. (Note that light in this context is described as consisting of particles, i.e., photons.) A typical absorption cross-section has units of cm 2 ⋅molecule −1.

  4. Speed of electricity - Wikipedia

    en.wikipedia.org/wiki/Speed_of_electricity

    The speed of this flow has multiple meanings. In everyday electrical and electronic devices, the signals travel as electromagnetic waves typically at 50%–99% of the speed of light in vacuum. The electrons themselves move much more slowly. See drift velocity and electron mobility.

  5. Cross section (physics) - Wikipedia

    en.wikipedia.org/wiki/Cross_section_(physics)

    Here ΔΩ is the finite angular size of the detector (SI unit: sr), n is the number density of the target particles (SI unit: m −3), and t is the thickness of the stationary target (SI unit: m). This formula assumes that the target is thin enough that each beam particle will interact with at most one target particle.

  6. Electromagnetic radiation - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_radiation

    As a wave, light is characterized by a velocity (the speed of light), wavelength, and frequency. As particles, light is a stream of photons. Each has an energy related to the frequency of the wave given by Planck's relation E = hf, where E is the energy of the photon, h is the Planck constant, 6.626 × 10 −34 J·s, and f is the frequency of ...

  7. Ionizing radiation - Wikipedia

    en.wikipedia.org/wiki/Ionizing_radiation

    Some particles can travel up to 99% of the speed of light, and the electromagnetic waves are on the high-energy portion of the electromagnetic spectrum. Gamma rays , X-rays , and the higher energy ultraviolet part of the electromagnetic spectrum are ionizing radiation, whereas the lower energy ultraviolet , visible light , infrared , microwaves ...

  8. The best air purifiers of 2025 - AOL

    www.aol.com/lifestyle/best-air-purifiers...

    Particle Removal is 99.97% down to 0.1 microns, plus this Energy Star-certified device boasts one of the highest Clean Air Delivery Rate (CADR) of 410 for fine smoke particles, dust and pollen ...

  9. Brownian motion - Wikipedia

    en.wikipedia.org/wiki/Brownian_motion

    In 1906 Smoluchowski published a one-dimensional model to describe a particle undergoing Brownian motion. [24] The model assumes collisions with M ≫ m where M is the test particle's mass and m the mass of one of the individual particles composing the fluid. It is assumed that the particle collisions are confined to one dimension and that it ...