Physics Glossary – L

Lamb Shift

There is a difference between the first two energy levels in the spectrum of hydrogen, this is called the Lamb Shift after the Willis Eugene Lamb.

Law of Conservation of Energy/Momentum

Energy/momentum cannot be created or destroyed; it may be changed from one form to another.

Law of Universal Gravitation

Gravitational force between two objects depends directly in the product of their masses and inversely on the square of their separation.


An optical device that produces very narrow beam of monochromatic (one wavelength), coherence (in the same phase) and intense light. It works by pumping electrons to a higher excited state, the electron fall back and give out very defined form of light. A laser was originally an acronym for “Light Amplification by Stimulated Emission of Radiation”.


A lepton (Greek for “light”, as opposed to hadrons which are “heavy”) is a subatomic particle that is not made of quarks. They include the electron, the muon, the tau, and their respective neutrinos.

Light Year

The distance light can travel in one year, roughly 10 million million kilometers. For example, the nearest known star, Proxima Centauri is 4.22 light years away.

Light Emitting Diode

Is a semiconductor device that emits incoherent monochromatic light when electrically biased in the forward direction. This effect is a form of electroluminescence. The color depends on the semiconducting material used, and can be near-ultraviolet, visible or infrared. Nick Holonyak Jr. developed the first practical visible-spectrum LED in 1962.

Latent Heat

Is the heat that is added to a system that changes the physical state of the substance e.g. changing from a light to a gas.

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