| Laser: | A device that produces coherent light by stimulated emission of radiation. |
| Latent heat of fusion: | The quantity of heat required to convert one unit mass of a substance from solid to the liquid state at its melting point without any change in its temperature. |
| Latent heat of sublimation: | The quantity of heat required to convert one unit mass of a substance from solid to gaseous state without any change in its temperature. |
| Latent heat of vaporization: | The quantity of heat required to convert one unit mass of a substance from liquid to gaseous state at its boiling point without any change in its temperature. |
| Law of Conservation of Energy: | Energy can neither be created nor destroyed, but can be transformed from one form to another. |
| Law of conservation of mass: | Mass can neither be created nor destroyed in a chemical reaction. |
| Law of conservation of momentum: | In the absence of external forces, the total momentum of a group of interacting objects remains constant. |
| Lenz's law: | The induced current always flows in such a direction that it opposes the cause producing it. |
| Light-year: | The distance traveled by light through empty space in one year, it is equal to 9.46 x 1012 km. |
| Longitudinal strain: | The ratio of change in length of a body to its initial length. |
| Longitudinal wave: | The particles of the medium oscillate in the direction of propagation of the wave. |
| Luminosity: | The total amount of energy radiated each second from the surface of a source. |
| Lyman series: | A group of lines in the ultraviolet region in the spectrum of hydrogen. |
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