L
Lamp
A device intended to produce light energy. Modern lamps convert electrical energy to light energy via one of two main mechanisms - the filament lamp or the gas discharge lamp.
Laser
The word laser was originally an abbreviation for Light Amplification by the Stimulated Emission of Radiation. Lasers have countless applications, many in medicine and communications. Lasers produce light which is monochromatic, coherent and tightly focussed. Lasers are used in the technique of photocoagulation (used to treat retinae).
Latent heat of vaporization
The heat absorbed when one gram of a substance changes from the liquid phase to the gaseous phase, or the heat released when one gram of gas changes from the gaseous phase to the liquid phase.
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) is called its latent heat of fusion (L). The SI unit of latent heat of fusion is J kg-1.
Latent heat
Latent heat, or hidden heat, is heat that is taken up and stored when a substance changes state from a solid to a liquid, from a liquid to a gas, or from a solid directly to a gas. It cannot be measured by a thermometer.
Law of Conservation of Energy
The law of conservation of energy states that energy may neither be created nor destroyed. Therefore the sum of all the energies in the system is a constant.
Law of conservation of mass
Same as law of conservation of matter; mass, including single atoms, is neither created nor destroyed in a chemical reaction.
Law of conservation of matter
Matter is neither created nor destroyed in a chemical reaction.
Law of conservation of momentum
The total momentum of a group of interacting objects remains constant in the absence of external forces.
Light
Anything that can travel from one place to another through empty space and can influence matter, but is not affected by gravity.
Light Dependent Resistor (LDR)
LDRs are designed so that their resistance depends on the intensity(brightness) of light falling on them.
Light Emitting Diode
LEDs are simply diodes which emit light when connected correctly to a power supply.
Light-year
The light-year (ly) is a unit of distance which is useful in astronomy. It is the distance which light (or any other form of electromagnetic radiation) travels in one year,approximately 9.5 x 10^11 km.
Line spectrum
Narrow lines of color in an otherwise dark spectrum.
Lines of force
Lines drawn to make an electric field strength map, with each line originating on a positive charge and ending on a negative charge; each line represents a path on which a charge would experience a constant force and lines closer together means a stronger electric field.
Liquids
A phase of matter composed of molecules that have interactions stronger than those found in a gas but not strong enough to keep the molecules near the equilibrium positions of a solid, resulting in the characteristic definite volume but indefinite shape of a liquid.
Liquid Crystal Display (LCD)
This is an output device. They run on almost no power since they don't produce their own light, but work by reflecting room or daylight.
Liter
A metric system unit of volume, usually used for liquids.
Logic Diagram
A simplified diagram of an electronic system, using rectangles to represent input and output devices along with the usual logic gate symbols for the AND, OR and NOT gate etc.
Logic Gate
Logic gates allow an electronic system to make decisions based on a number of inputs. For example an OR gate can be used to illuminate a warning light if engine temperature is too high or if it is over-revved.
Logic State
In a digital system, there are two logical states. One state is 'ON', 'HI' or 'logic 1' (all mean the same). The other is 'OFF', 'LOW', 'logic 0' (again all mean the same).
Longitudinal waves
The wave in which the particles of the medium oscillate along the direction of propagation of wave is called the longitudinal wave. Sound waves are longitudinal waves.
Long-sighted
A problem with the accommodation ability of an eye. Basically, the eye can focus on far away objects with no problem, but can't properly focus on nearby objects. There can be two causes of this. The first occurs in older people, where the aging eye lens becomes less flexible and so cannot adopt the highly curved shape needed to focus at short range. This condition is called presbyopia. The second cause is that retina is too near to the lens - so that the focal point falls behind the retina. This is called hypermetropia or hyperopia. Long-sightedness can be treated by wearing spectacles which are convex in shape and therefore help to focus the image properly by reducing the overall focal length of the glasses and eye.
Lorentz transformation
The transformation between frames in relative motion.
Loudness
A subjective interpretation of a sound that is related to the energy of the vibrating source, related to the condition of the transmitting medium, and related to the distance involved.
Lubricant
A lubricant is a substance which reduces friction between two surfaces. Examples are oil, water, air, bananas, seaweed.
Luminosity
The total amount of energy radiated into space each second from the surface of a star.
Luminous
An object or objects that produce visible light; for example, the sun, stars, light bulbs, and burning materials are all luminous.