Physics Glossary – F

Field Effect Transistor (FET)

A type of transistor commonly used for amplifying weak-signal. The current flows down the channel between the source (source of electrons) and the drain. The amount of current that flows is regulated by the “Gate”, a small change in the voltage at the gate can increase the current flow in the channel dramatically.

Fissile Material

Isotopes which can undergo nuclear fission. Example of fissile materials are Uranium-233, uranium-235, plutonium-239, plutonium-241.


Is a nuclear process in which a heavier unstable nucleus divides or splits into two or more lighter nuclei, with the release of substantial amounts of energy. When a free neutron of the proper energy is captured by the nucleus of a fissionable atom, the resulting unstable nucleus will split producing two or more fission products (atomic nuclei of different elements formed from the protons and neutrons originally comprising the nucleus before its fission), two or three free neutrons and a tremendous amount of energy.


The rate of flow of mass or energy per unit area in a certain direction. This means the amount of energy that is flowing out from a source e.g. as a blub gives off energy its flux changes depending on how far from the source you are

Flux Density

The amount of flux per unit of cross-sectional area. The derived SI unit for magnetic flux density is the Tesla.

Foucault pendulum

Is a tall pendulum free to oscillate in any vertical plane and capable of running for hours. It is used to demonstrate Coriolis force and the rotation of the earth. It is named after the inventor, Léon Foucault. A Foucault pendulum at the equator does not rotate. A pendulum at the pole rotates once a day. A pendulum anywhere on the earth rotates with a speed proportional to the sine of its latitude; thus one at 45° rotates once every 1.4 days and one at 30° every 2 days.


Is a process where two small nuclei join together to form a larger nucleus. Nuclear fusion is the energy source that causes stars to shine, and is one of the processes in the hydrogen bomb.