**Fabry
Perot Interferometer**

An interferometer
made of a transparent plate with two reflecting surfaces or two parallel highly
reflecting mirrors. It is named after Charles Fabry & Alfred Perot. It
makes use of multiple reflections between two closely spaced partially silvered
surfaces. Part of light is transmitted each time the light reaches second
surface, resulting in multiple offset beams which can interfere with each
other. The large number of interfering rays produces an interferometer with
extremely high resolution, somewhat like multiple slits of all diffraction
grating increase its resolution.

**Face
Centered Cubic structure(FCC)**

The crystal
structure found for many metals has a unit cell of cubic geometry, with atoms
located at each of the corners and the centers of all cubic faces.

**Fahrenheit
Scale**

Temperature scale introduced by German
physicist Daniel Gabriel Fahrenheit in 1724. On this scale, the freezing point
of water is 32 degree Fahrenheit and boiling point 212 degree Fahrenheit at
standard atmospheric pressure. This puts boiling and freezing points of water
exactly 180^{o} apart. Therefore a degree on Fahrenheit scale is 1/180
of interval between freezing and boiling point. A temperature interval of 1^{o}F
is equal to an interval of 5/9 ^{o}C.

**Farad
**

It
is SI unit for capacitance. It is named after English Physicist Michael
Faraday. A capacitor is said to have one Farad value when one coulomb of stored
charge causes a potential difference of 1 Volt across its terminals.

1Farad = 1 Coulomb / Volt.

**Faraday
Effect **

The rotation of
plane of polarization of a light beam when plane polarized light is passed
through a substance in a magnetic field; the direction of travelling of light
is parallel to magnetic lines of force. For a given substance, the rotation is
proportional to thickness traversed by light and to the magnetic field
strength.

**Faraday’s
Constant**

The total charge
carried by 1 mole of electrons is given by 96487 Cmol^{-1}. The quantity is
known as Faraday constant.

**Faraday’s
Law of Electrolysis**

The quantitative relationships between
electricity and chemical change where first described by Michael faraday in
1830. These are

i) The
mass of a chemical substance involved at an electrode is directly proportional
to quantity of electricity passed through the cell.

ii)The
mass of different substances produced by a given quantity of electricity are
proportional to equivalent mass of substances.
** **

Mathematical representation

a) m α Q b)
m α M/v_{e}

where ‘m’ represents mass of substance deposited at
cathode; ‘M’ represents molar mass of substance; v_{e} denotes stoichometric number of electrons in reaction
involving reduction/oxidation of chemical species at respective electrode of
electrolytic cell.

**Faraday’s
law of Electromagnetic Induction**

It states that induced emf in a closed circuit
is equal to negative rate at which magnetic flux through it changes.

**Fast
Neutrons**

Neutrons
possessing high kinetic energies in the million electron volt range are called
fast neutrons.

**Fathom(ftm)**

It is a unit of
length used especially for measuring depth of water. 1 ftm = 1.8288
meters.

**Fault**

Places where rock
structures have broken apart and can slide past each other are called faults.

**Feedback**

The process of
injecting a portion of output energy of some device to the input is known as
feedback.

**Femto**

It is a prefix in the metric system
denoting a factor of 10^{-15}.

**Fermat’s
Principle of Extremum Path**

Fermat, in 1658,
postulated that “a ray of light in passing from one point to another by any
number of reflections or refractions chooses a path along which the time taken
is least or extremum.

**Fermi
Dirac Statistics**

Statistics
proposed by Fermi & Dirac. The postulates are as follows:

i) Applicable
to identical & indistinguishable particles with spin odd multiple of half,
such as electrons, protons, neutrons etc, which are called the Fermions;

ii) The minimum volume of a
phase cell is h^{3}, so the number of phase cells cannot be increased.

iii) No new
microstate is obtained by the interchange of position of particles in a cell.

iv)There
cannot be more than one particle in a cell i.e. Pauli’s exclusion principle is
obeyed.