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Online Physics Glossary / Terms / Dictionary

Physics Definitions Start from F

Flare (Solar) - Rapid release of energy from a localized region on the Sun in the form of electromagnetic radiation, energetic particles, and mass motions.

Flare Star - A member of a class of stars that show occasional, sudden, unpredicted increases in light. The total energy released in a flare on a flare star can be much greater that the energy released in a solar flare.

Footpoint - The intersection of magnetic loops with the photosphere.

Free Electron - An electron that has broken free of it's atomic bond and is therefore not bound to an atom.

Frequency - The number of repetitions per unit time of the oscillations of an electromagnetic wave (or other wave). The higher the frequency, the greater the energy of the radiation and the smaller the wavelength. Frequency is measured in Hertz.

Factor-label method - Dimensional analysis.

Farad - Unit of capacitance. One coulomb per volt.

Ferromagnetic Materials - Materials in which large internal magnetic fields are generated by cooperative action of electrons.

First Harmonic - In music, the fundamental frequency.

First law of Thermodynamics - Change in internal or thermal energy is equal to heat added and work done on system. Same as law of conservation of energy.

Fluid - Material that flows, i.e. liquids, gases, and plasmas.

Focal Length - Distance from the focal point to the center of a lens or vertex of a mirror.

Focal Point - Location at which rays parallel to the optical axis of an ideal mirror or lens converge to a point.

Forbidden Gap - Energy values that electrons in a semiconductor or insulator may not have.

Force - Agent that results in accelerating or deforming an object.

Frame of Reference - Coordinate system used to define motion.

Fraunhofer Lines - Absorption lines in the sun’s spectrum due to gases in the solar atmosphere.

Friction - Force opposing relative motion of two objects are in contact.

Fundamental Particles - Those particles( i.e. quarks and leptons) of which all materials are composed.

Fundamental Tone - Lowest frequency sound produced by a musical instrument.

Fundamental Units - Set of units on which a measurement system is based( i.e. meter, second, kilogram, ampere, candela).

Fuse - Metal safety device in an electric circuit that melts to stop current flow when current is too large.

Fusion - Combination of two nuclei into one with release of energy.

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