**Laboratory
Frame of Reference **

Frame
of reference, the centre of the coordinate system which lies on the laboratory
in which experiment is done.

or

The
frame of reference in which laboratory measurement devices are at rest is
usually referred as laboratory frame of reference.

**Lambda
Particle **

It is a elementary
particle, which is neutral and discovered in cloud chamber experiments, having
life time of order 10^{-10} sec and has rest energy of about 1115 MeV.
It doesn’t conserve parity and has spin- 1/2. It belongs to class of Hyperons.

**Lambda
Point**

When Helium is
cooled to a critical temperature of 2.17 K (called its lambda point),
a remarkable discontinuity in heat capacity occurs, the liquid density drops,
and a fraction of the liquid becomes a zero viscosity "superfluid".
Super fluidity arises from the fraction of helium atoms which has condensed to
the lowest possible energy. In simple terms, the Lambda point is the
temperature below which normal fluid Helium (Helium-I) transitions to super fluid
Helium-II

**Lambert
**

The unit of
brightness or luminance in CGS system, equivalent to brightness of a perfectly
diffusing surface that emits or reflects one Lumen per square centimeter.
1Lambert (L) = 1/π Candela/cm^{2}.

**Lambert’s
Law of Absorption **

Each layer of
equal thickness absorbs an equal fraction of light which traverses it.

**Lambert’s
Law of Illumination **

The illumination
of a surface on which light falls normally from a point source is inversely
proportional to square of distance of surface from source. If the normal to
surface makes an angle with direction of rays, illumination is proportional to
cosine of that angle.

**Lambert’s
law**

Law
which describes the attenuation of intensity of electromagnetic wave inside a
medium is called as Lambert’s law.

**Laminar
Flow **

It is type of
fluid flow in which the fluid travels in regular paths. In laminar flow,
sometimes called streamline flow, the velocity, pressure and other flow
properties at each point in the fluid remain constant.

**Laplace
Equation**

It is a
mathematical equation which gives the divergence of the gradient of a function.** **Laplace’s
equation is a second-order partial differential equation widely useful in physics because
its solutions (known as harmonic
functions) occur in problems of electrical, magnetic, and
gravitational potentials, of steady-state temperatures, and of Hydrodynamics.
The equation was
discovered by the French mathematician and astronomer Pierre-Simon
Laplace (1749–1827).

**Larmor’s
Precession**

When an atom is
placed in an external magnetic field, the electron orbit precesses about the
direction of external magnetic field. There will be change in angular velocity
of electron without any change in form of orbit.

**LASER**

It is acronym for
Light Amplification by Stimulated Emission of Radiation. It is that device
which produces an intense, monochromatic, coherent and unidirectional light
beam is obtained. It was discovered in 1950, by Town & Shallow. LASER
produces a light beam in which all the waves are of same frequency.

**Latent
Heat (Heat of Transformation)**

The
amount of energy per unit mass that must be transferred as heat when a sample
completely undergoes phase transition.

(or)

The
amount of heat needed to change the state of a given substance without any
change in temperature.

**Latent
Heat of Fusion**

The quantity of
heat necessary to change one gram of solid to liquid without change of
temperature, measured as calories per gram.

**Latent
Heat of Sublimation**

The heat absorbed
by one gram or unit mass of a substance in the process of changing from a solid
to a gaseous state, at a constant temperature and pressure.

**Latent
Heat of Vaporization**

The quantity of
heat necessary to change one gram of liquid to vapor without change of
temperature, measured as calories per gram.

**Lateral
Chromatic Aberration**

The difference in length of red and violet
images for an object at finite distance is called lateral chromatic vibration.