Light
Light is a
form of electromagnetic radiation composed of wave packets of energy. Light is
the only thing that can make anything visible. Light is composed of photons a
category of quantum particles that have no mass. Many theories have been over
time in respected to light. The visible light has a spectrum that is called as
electromagnetic spectrum. Every visible wave should have a low frequency of
radiation. The visible form of light is having a wavelength in the range of 400
nanometers (nm), or 400×10−9 m, to 700 nanometres –
between the infrared, with longer wavelengths and the ultraviolet, with shorter
wavelengths.
The basic properties of visible light are-
·
Intensity- the intensity of light is defined as the density and
power of energy.
·
Frequency- The frequency of light is the frequency of the
propagated wave.
·
Propagation in a direction- The direction of way of light.
Optics
The
study of light and its applications is known as optics.
Refraction
An example of refraction of
light. The straw appears bent, because of refraction of light as it enters
liquid from air.
Refraction
is the bending of light rays when passing through a surface between one
transparent material and another. It is described by Snell's Law:
where
is the angle between the ray and the surface normal
in the first medium,
is the angle between the ray and the surface normal in the
second medium, and n1 and n2 are the indices of
refraction, n = 1 in a vacuum
and n > 1 in a transparent substance.
When a
beam of light crosses the boundary between a vacuum and another medium, or
between two different media, the wavelength of the light changes, but the
frequency remains constant. If the beam of light is not orthogonal
(or rather normal) to the boundary, the change in wavelength results in a
change in the direction of the beam. This change of direction is known as refraction.
The
refractive quality of lenses
is frequently used to manipulate light in order to change the apparent size of
images. Magnifying glasses,
spectacles, contact lenses, microscopes and refracting telescopes
are all examples of this manipulation.
Nomenclature
Strong
spectral lines in the visible part of the spectrum often have a unique
Fraunhofer line designation, such as K for a line at 393.366 nm
emerging from singly ionized Ca+, though some of the Fraunhofer
"lines" are blends of multiple lines from several different species.
In other cases the lines are designated according to the level of ionization
adding a Roman numeral to the designation of the chemical element, so that Ca+
also has the designation Ca II. Neutral atoms are denoted with the roman
number I, singly ionized atoms with II, and so on, so that for example Fe IX
(IX, roman 9) represents eight times ionized iron. More detailed designations
usually include the line wavelength and may include a multiplet number (for atomic lines) or
band designation (for molecular lines). Many spectral lines of atomic hydrogen
also have designations within their respective series, such as the Lyman series
or Balmer series.
Quantum
theory
In 1900 Max Planck, attempting to
explain black body radiation suggested that although light was a wave, these
waves could gain or lose energy only in finite amounts related to their
frequency. Planck called these "lumps" of light energy
"quanta" (from a Latin word for "how much"). In 1905,
Albert Einstein used the idea of light quanta to explain the photoelectric
effect, and suggested that these light quanta had a "real" existence.
In 1923 Arthur Holly Compton showed that the wavelength shift seen when low
intensity X-rays scattered from electrons (so called Compton scattering) could
be explained by a particle-theory of X-rays, but not a wave theory. In 1926
Gilbert N. Lewis named these liqht quanta particles photons.
Eventually the modern theory of
quantum mechanics came to picture light as (in some sense) both a
particle and a wave, and (in another sense), as a phenomenon which is neither
a particle nor a wave (which actually are macroscopic phenomena, such as
baseballs or ocean waves). Instead, modern physics sees light as something that
can be described sometimes with mathematics appropriate to one type of
macroscopic metaphor (particles), and sometimes another macroscopic metaphor
(water waves), but is actually something that cannot be fully imagined. As in
the case for radio waves and the X-rays involved in Compton scattering,
physicists have noted that electromagnetic radiation tends to behave more like
a classical wave at lower frequencies, but more like a classical particle at
higher frequencies, but never completely loses all qualities of one or the
other. Visible light, which occupies a middle ground in frequency, can easily
be shown in experiments to be describable using either a wave or particle
model, or sometimes both.
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The Rutherford–Bohr
model of the hydrogen atom (Z = 1) or a hydrogen-like ion (Z
> 1), where the negatively charged electron confined to an atomic shell
encircles a small, positively charged atomic nucleus and where an
electron jump between orbits is accompanied by an emitted or absorbed amount of
electromagnetic energy (hν).[1] The orbits in which the
electron may travel are shown as grey circles; their radius increases as n2,
where n is the principal quantum number. The 3 → 2 transition
depicted here produces the first line of the Balmer series, and for hydrogen (Z
= 1) it results in a photon of wavelength
656 nm
(red light).
Taken
reference from internet
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