Spectrum
Introduction
A spectrum is a condition that is not limited to a specific set of
values but can vary, without steps, across a continuum.
The word was first used scientifically in optics to describe the rainbow of colours in visible light after passing through a prism. As scientific understanding of light advanced, it came to apply to the entire electromagnetic spectrum.
In the 17th century, the word spectrum was introduced into optics by Isaac Newton, referring to the range of colours observed when white light was dispersed through a prism. Soon the term referred to a plot
of light intensity or power as a function of frequency or wavelength, also known as a spectral density plot.
The term spectrum was expanded to apply to other waves, such as sound waves that
could also be measured as a function of frequency, frequency spectrum and power spectrum of a
signal.
Electromagnetic
spectrum
Electromagnetic spectrum refers to
the full range of all frequencies of electromagnetic radiation and also to the characteristic
distribution of electromagnetic radiation emitted or absorbed by that
particular object. Devices used to measure an electromagnetic spectrum are
called ‘spectrograph’ or ‘spectrometer’. The visible spectrum is the
part of the electromagnetic spectrum that can be seen by the human eye. The wavelength of visible light
ranges from 390 to 700nm.
The absorption spectrum of a chemical element or chemical compound is the spectrum of frequencies or wavelengths of incident
radiation that are absorbed by the compound due to electron transitions from a
lower to a higher energy state.
Light from many different sources
contains various colours, each with its own brightness or intensity. A rainbow,
or prism, sends these component colours in
different directions, making them individually visible at different angles. A
graph of the intensity plotted against the frequency is the frequency spectrum
of the light. When all the visible frequencies are present equally, the
perceived colour of the light is white, and the spectrum is a flat line.
In radio and telecommunications, the
frequency spectrum can be shared among many different broadcasters. The radio spectrum is the part of the electromagnetic spectrum corresponding to frequencies lower
below 300 GHz, which corresponds to wavelengths longer than about
1 mm. The microwave spectrum corresponds to frequencies
between 300 MHz (0.3 GHz) and 300 GHz and wavelengths
between one meter and one millimeter.
Mass
spectrum
A plot of ion abundance as a
function of mass to charge ratio is called a mass spectrum. It can
be produced by a mass spectrometer instrument. The mass spectrum can be used to determine the quantity and mass of atoms and molecules.
Energy
spectrum
In physics, the energy spectrum of a
particle is the number of particles or intensity of a particle beam as a
function of particle energy. Examples of techniques that produce an energy
spectrum are alpha particle spectroscopy, electron energy loss spectroscopy,
and mass analyzed ion kinetic energy spectrometry.
Discrete
spectrum
In physics, particularly in quantum mechanics, some differential operator have discrete spectra, with gaps between
values. Common cases include the Hamiltonian and the angular momentum operator.
Spectrogram
In acoustics, a spectrogram is a visual representation of the
frequency spectrum of sound as a function of time or another variable. An apparatus used for recording and measuring
spectra, especially as a method of analysis.
Splitting of white light
Light changes speed as it moves from one medium to another (for example,
from air into the glass of the prism). This speed change causes the light to be refracted and to enter the new medium at a different angle. The degree of bending of the
light's path depends on the angle that the incident beam of light makes with the surface, and on the ratio between the refractive indices of the two media.
Light of different colours to be refracted differently and to leave the
prism at different angles, creating an effect similar to a rainbow.
This can be used to separate a beam of white light into its constituent spectrum of colours.
Reference
·
Wikipedia
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