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Fraunhofer
Lines
When sun’s light
is allowed to fall on slit of a spectrometer, its spectrum is found to consist
of many dark lines. The lines are called Fraunhofer lines. The number of lines
is approximately 700. These lines are due to absorption of certain wavelengths
in sunlight by gases in sun’s outer sphere.
Fraunhofer’s
Diffraction
Type of
diffraction in which light rays from a source of light kept at a finite
distance are made incident on obstacle or aperture in form of a parallel beam
by using a convex lens. The source is placed in focal plane and convex lens.
The light rays diffracted by obstacle or aperture are focused on a screen kept
at a finite distance by means of another convex lens with which screen is
placed in its focal plane. The diffraction pattern in this is the image of
source.
Free
Electron
Electron which is
not bounded to any atom or molecule or ion and moves freely in crystal
structure under influence of constant electric potential is termed as free
electron.
Free
Fall
It is motion of a body due to only
gravitational force acting on it. Freely falling bodies doesn’t get influenced
by air resistance and they accelerate downwards with 9.8m/sec.
Free Oscillation
The oscillation
of a physical system with its natural frequency and under no external influence
other than impulse that initiated the motion is called as free oscillation.
Free
Vibration
When a particle
vibrates continuously under no external force such as friction etc, then such
vibration is called free vibration.
Freezing
Point
The temperature,
at which vapor pressure of solid phase of a substance becomes equal to vapor
phase of its liquid phase, is known as freezing point of a substance.
Frenckel
Defect
The type of
defect in crystalline ionic substance, in which, the ion, instead of being in
its expected location, is found in one of the interstices. Frenckel defects are
more common in ionic crystals where size of cation is such that it can be
accommodated in interstitial sites.
Frequency
Modulation
Type of
modulation in which frequency of carrier wave is changed in accordance with
intensity of the signal without changing amplitude.
Frequency
The rate at which
an event occurs over a particular period of time or in given sample is called
frequency. It can also be defined as number of cycles per unit time.
Fresnel
Biprism
Optical device
consisting of two prisms of very small refracting power, set base to base and
which forms two images of a single source. It is often used to produce
interference fringes.
Fresnel’s
Diffraction
The type of
diffraction formed when source of light or the screen on which diffraction
pattern formed or both are at a finite distance from the obstacle or aperture.
The incident wave front may be plane, spherical or cylindrical. The diffraction
pattern is the image of obstacle or aperture.
Friction
Friction is
tangential force between the contact surfaces of two bodies.
Full
Moon
Full moon is when the sun and the moon are
facing opposite, being in opposite direction from an earth perspective. A full
moon is the lunar phase that
occurs when the Moon is completely illuminated as seen
from the Earth.
Full
Wave Rectifier
Device in which
current flows through the load in some direction for both half cycles of input
ac voltage is called full wave rectifier.
Fundamental
Frequency
Lowest frequency
of periodic wave function is termed as fundamental frequency.
Fundamental
Particles
The word
fundamental implies that the particles are basic building blocks of matter.
They are nothing but quanta of corresponding field. Study of fundamental
particles is basis to understand radiation phenomena. We may regard any
radiation as a flux of elementary particles.
Fundamental
Quantity
The physical
quantity which does not depend on other quantities is known as fundamental
quantity.
Fundamental
Unit
The unit used to
measure fundamental quantity is called fundamental unit.
Fusion Bomb
See hydrogen bomb.
