Laminar flow – a type of fluid flow in which the layers move smoothly past each other without crossing paths (see streamline)

Laser – a coherent, monochromatic (almost), intense light source resulting from stimulated emission (acronym for Light Amplification by Stimulated Emission of Radiation)

Lateral magnification – the ratio of the image height to the object height

Law of Charles and Gay-Lussac – for a gas at constant pressure, the volume is proportional to the absolute temperature (see equation 12.3)

Law of conservation of charge – states that the total amount of electric charge in the universe remains constant

Law of conservation of mechanical energy – if the forces are all conservative, the sum of the kinetic and potential energies is a constant

Law of reflection - When light travels from a less dense to a more dense optical material, the rays are bent toward the normal. When a light ray travels from a more dense to a less dense optical material, the rays are bent away from the normal.

Law of refraction - also called Snell's law. When light travels from a less dense to a more dense optical material, the rays are bent toward the normal. When light rays travel from a more dense to a less dense optical material, the rays are bent away from the normal. The bending occurs at the boundary, or interface, between the two material.

Law of universal gravitation – states that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them

Length contraction – (also known as Lorentz contraction) the length of an object measured by an observer in motion relative to the object will be shorter than its proper length (see equation 25.3)

Lenz’s law – states that the direction of an induced current is such that its own magnetic field opposes the original change in magnetic flux that induced the current (see figure 20.5)

Leptons - elementary particles that interact by the weak nuclear force (see table 32.1)

Linear momentum – the product of mass and velocity

Linear thermal expansion – relative change in length in direct proportion to change in temperature

Linear thermal expansion coefficient – the relative change in length per unit change in temperature for linear thermal expansion (see equation 11.3)

Lines of force– a diagram of continuous lines drawn to illustrate the direction of a force on a test mass, or charge (also called field lines)

Liquid crystal– a class of material in which the regular periodic arrangement exists in only one or two dimensions

Lodestone - Lodestone is found in most parts of the world and is usually in the form of magnetite (Fe₃O₄). Large deposits were found in Asia Minor, near an ancient town named Magnesia. These rocks became known as magnesia rocks and later as magnets.

Longitudinal wave – the particles of the wave medium move back and forth along the direction of the propagation of the wave