Physics Glossary – I


A form of camera tube in which a beam of high-velocity electrons scans a photoemissive mosaic. It was invented by Vladimir Zworykin in 1923, and used in electronic TV broadcasting from 1939 until it was replaced by more advanced tubes.


Is an object’s tendency to resist changes in its state of motion. Therefore if it is at rest or moving at a constant velocity, it takes a force to overcome the objects inertia. The measure of inertia is the objects mass.


An instrument that works on the principle that two waves that coincide with the same phase will amplify each other while two waves that have opposite phases will cancel each other out. It can be used to determine the wavelength of light, measurement of the diameter of stars and many other uses.


An electrically charged molecule or atom is known as an ion because it has gained or lost electrons from its normal complement, a process known as ionization.

Ion Engine

Is a type of spacecraft propulsion that uses beams of ions for propulsion, accelerated by passing them through highly-charged grids (similar in concept to a vacuum tube). This acceleration is very efficient, and ion thrusters can deliver performance several orders of magnitude greater than traditional rocket engines.


Is the part of the atmosphere that is ionized by solar radiation, and too tenuous to be cooled by contact with other air. It forms the inner edge of the magnetosphere and has practical importance because it reflects radio waves to distant places on Earth.


Isotopes of a chemical element are atoms whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope meaning at the same place, is due to the fact that isotopes are located at the same place on the periodic table.

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