A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

**Fluidity**

It is physical
property of a substance which makes it to flow. The molecules of such substance
move one past other. The substance assumes the shape of its container.

**Fluorescence**

Phenomenon of
luminescence in which emission of light occurs during excitation or within 10^{-8}
Sec after the excitation source is removed.

**Fluorescent
Lamp **

Lamp contains a
tube filled with inert gas & a small amount of mercury vapor (low
pressure). It doesn’t have filament running through it instead they are
equipped with coiled Tungsten filaments coated with an electron emitting
substance. The fluorescent light occurs in two stages. First, electrons emitted
from cathodes create an electrical arc through Mercury vapor. Then the
resultant UV radiation strikes Phosphor coating which then gives off visible
light.

**Flux
(Energy)**

The energy flux
is a measure of the total energy incident on a surface per unit area per unit
time. Another term used for this quantity especially in dosimetry, is the
energy fluence rate.

**Flux
(particle)**

Particle flux
simply represents the number of particles incident on a surface per unit area
per unit time. In the field of dosimetry, this quantity is also known as
particle fluence rate.

**Focal
length**

The distance from
the lens to that point where light rays converges or diverges (depends on type
of lens). Focal length decides the lens strength/power. Lens power is inversely
proportional to focal length.

**Focal
point**

Focal points are
a pair of points on principal axis of a system such that all rays starting from
one focal point, after passing through the system, become parallel to the
principal axis and parallel rays after refraction through the optical system
converge at second focal point. First point is object point on principal axis
for which the image point is at infinity and the second focal point is the
image point on principal axis for which object point is at infinity.

**Focaults
Pendulum**

It is a device used
to demonstrate the rotation of earth and the fact that earth is not an inertial
frame of reference.

**Focus**

The
place in the earth crust, where the vibrations come from, is called focus of
earth quake.

**Force
**

Mass of an object
times the acceleration it gained.

**Forced
Vibration**

This is vibration
of the body which exists because of exertion of external periodic force
constantly on body.

**Forward
Bias**

Term used in
solid state physics. It is state of biasing P-N junction where ‘P’ junction is
at higher potential compared to ‘N’ junction. This type of biasing reduces
width of depletion Layer in P-N junction and the diode conducts electrically.

**Forward
Biased Diode**

The ‘P’ junction of P-N diode is kept at high potential and ‘N’ junction at low potential.

**Fourier
Theorem **

Fourier theorem
deals with the summation of a number of simple harmonic vibrations in which the
vibrations are in the same straight line. The theorem also helps in the
synthesis and analysis of complex forms of vibrations. This theorem was
formulated by J.B.T Fourier in 1828. The theorem states that any finite,
continuous and single valued periodic function can be expressed as summation of
number of simple harmonic terms (sine and cosine functions) having the
frequencies integer multiple of given function. Fourier’s theorem deals primarily with the
synthesis of a complex periodic vibration from simple harmonic terms and it
gives a method to analyze a complex vibration into its component vibrations.

**Frame
of Reference**

It is a
coordinate system relative to which we describe the motion of body.

**Franck
& Hertz Experiment**

It is the
experiment which revealed the existence of discrete stationary states of
electrons.

**Franck-Condon
Principle**

According to this
principle, an electronic transition takes place so rapidly that a vibrating
molecule doesn’t change its inter nuclear distance appreciably during the
transition. That is during an electronic transition, inter-nuclear distance
remains the same, means straight line representing a transition between
electronic states will be vertical. Transition between electronic states occurs
vertically in a potential energy diagram.

**Frank-Hertz
Experiment**

Experiment which was carried out by James Frank and Gustav Hertz in 1914 which revealed directly the existence of discrete quantized stationary energy states of electrons.

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