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Understanding Spectra

Last updated date: 17th Mar 2023
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A spectrum (plural: spectra) could be a range of bands of colours that appear when light passes through a prism or water drops. The simplest example of a spectrum could be a rainbow. There are 3 kinds of atomic spectra and they are emission spectra, absorption spectra, and continuous spectra. Each spectrum holds a large variety of data. For example, there are many alternative mechanisms by which an object, such as a star, can produce light. Features of those mechanisms incorporate a characteristic spectrum. 

Spectroscopy is very useful in helping scientists understand how an object like a black hole, star, or active galaxy produces light, how fast it's moving, and what components it's composed of. 

What is Spectrum?

The distinctive electromagnetic radiation wavelengths that are released or absorbed by an object or substance, atom, or molecule are known as the spectrum.

Nature makes a stunning spectrum we tend to call rainbows. Sunlight passing through raindrops is spread out to display its varied colours, the different colours are simply the way our eyes perceive radiation with slightly different energies. 

A spectrum is just a chart or a graph that shows the intensity of light being emitted over a range of energies. It ranges from the longest radio waves to the shortest X-rays and gamma rays. These invisible waves enable us to make calls from our mobile devices, use the internet, call a cab, pull up directions to a destination, and do everything on our mobile devices. Thus, the frequencies we tend to use for wireless communication are also a part of the electromagnetic spectrum.

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Emission Spectra 

Types of Spectrum

An instrument designed for visual observation of spectra is named a spectroscope and the photographs are a spectrograph. Spectra are also classified according to the character of their origin—i.e., emission or absorption.

Some of the spectra are listed below :

  1. Electromagnetic spectrum

  2. Emission spectrum

    1. Continuous spectra 

    2. Discontinuous spectra

  3. Absorption spectrum

Electromagnetic Spectrum: The electromagnetic (EM) spectrum is the range of all kinds of EM radiation. The visible radiation from a lamp to the rays used to figure out a fractured bone, all are electromagnetic radiation. Also, the series of these totally different radiations is named the electromagnetic spectrum. 

range of all kinds of radiations.

Electromagnetic Spectrum

Emission Spectra: The spectrum obtained by the radiation emitted by a substance that has absorbed energy is named emission spectra. There are 2 kinds of emission spectrum: continuous spectrum and discontinuous spectrum.

  • Continuous Spectrum: This spectrum contains all wavelengths of light in a bound range. Hot, dense light sources like stars, as an example, emit an almost continuous spectrum of light that travels out in all directions and interacts with different materials in space. The broad range of colours that a star emits depends on its temperature. 

  • Discontinuous Spectrum: A discontinuous spectrum may be a type that contains gaps, holes, or breaks in terms of the wavelengths that it contains. Depending on the type of lines obtained, a discontinuous spectrum will be categorised into the following:

  • Line spectra or atomic spectra

  • Band spectra or molecular spectra

 continuous spectrum, emission spectrum, absorption spectrum.

Continuous Spectrum

Absorption Spectrum: It is formed by electromagnetic radiation that has passed through a medium in which radiation of specific frequencies is absorbed. In an absorption spectrum, parts of a continuous spectrum seem like dark lines or gaps. These dark lines indicate that the wavelengths are absorbed by the medium through which the light has passed. An absorption spectrum shows us which wavelengths of light were absorbed by a specific gas.  It's like a continuous spectrum, or rainbow, with some black lines.

Line Spectrum 

An electron in the excited state when making the transition to lower energy states, the light of fixed wavelengths is emitted. These emitted wavelengths seem as sharp bright lines within the dark background forming a spectrum. This is often called the line emission or discontinuous spectrum. As electrons responsible for producing such a spectrum are a part of the atom, line spectra are also known as atomic spectra. Inert gases, metal vapours, and atomised non-metals form this type of spectra. The spectrum of the elements may be a “characteristic property” of the elements and is commonly termed as “fingerprints” of the elements.

Band Spectrum 

This spectrum is given by hot metals and molecular non-metals. In this form of spectra discontinuity or gaps are seen between the bands or closely spaced bright lines. It's a characteristic property shown by molecules.

The key difference between continuous and line spectra is that the continuous spectrum contains all the wavelengths in a very given range whereas the line spectrum contains only a couple of wavelengths.

Uses of Spectrum

Electromagnetic Spectrum

  1. Gamma Rays: These rays are used to sanitise medical instrumentation and inhibit the growth of microorganisms.

  2. X-rays: These rays are used to visualise the inside of a body while not creating an incision. These rays are used for scanning functions.

  3. Ultraviolet Light: These rays kill microbes, therefore are used extensively to disinfect instrumentation.

  4. Visible Light: These rays facilitate us to visualise things around us.

  5. Infrared ays: As these rays will simply penetrate the skin, they are used widely in cosmetic applications. It's used in remote controls, electrical hearts, and thermal cameras.

  6. Microwave: It is widely used in microwave ovens to transmit the thermal energy required to cook food. Additionally used to guide aeroplanes.

  7. Radio Waves are used in radio and television broadcasts.

Moreover, atomic absorption spectroscopic analysis is used for deciding the atomic structure of a sample, characterization of macromolecules, space exploration, and many more.

Interesting Facts

  • A human eye can see a wavelength that ranges between 390 to 700 nm.

  • The wavelength of light varies by its type.

  • Our eyes acknowledge each wavelength by a distinct colour. Red colour has the longest and violet has the shortest wavelength.

  • Cones in human eyes work as a receiver for these tiny visible light waves.

  • Some other creatures can see components of the spectrum that aren't visible to us. For instance, some insects can see UV light.


Important Question

1. Name the objective property of a given colour once it undergoes refraction.

a) Frequency

b) refractive index

c) Wavelength

d) velocity

Ans: (c) Frequency

2. Name electromagnetic waves which will go through a quartz prism.

a) UV rays

b) Gamma rays

c) visible light

d) Infrared rays

Ans: (a) UV rays


From this article, we are able to conclude that we are continuously under the impact of electromagnetic radiation. From warming ourselves under the sun throughout winter to tuning our radio, to watching TV, sending a text message, or popping popcorn in a microwave, we are using electromagnetic energy. We rely on this energy each hour of each day. Without it, the world we all know couldn't exist at all.

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FAQs on Spectrum

1. What is the H spectrum?

Hydrogen gas radiates when subjected to an electric discharge during a discharge tube below low pressure. The radiation emitted by the atom is analysed with the help of a spectrograph. It's found to consist of a series of sharp lines within the UV, visible, and IR regions. This series of lines is known as the line or atomic spectrum of H. The lines within the visible region may be directly seen on the photographic film. The entire spectrum consists of six series of lines which are the Lyman, Balmer, Paschen, Brackett, Pfund, and Humphrey series. 

2. What is the explanation for the line broadening and shift in spectra?

There are several effects that control spectral line shape. A spectral line extends over a frequency range but not a single frequency. These reasons are: broadening as a result of local conditions and broadening as a result of extended conditions. Broadening occurs despite the local conditions because of the effects around the emitting component during a small area, Broadening because of the extended conditions could result from changes to the spectral distribution of the radiation. It can also result from the combining of radiation from a lot of regions that are far away from one another.

3. How can we study astronomy for stars from a spectrum?

From spectral lines, one can verify not only the component but the temperature and density of that component within the star. The breadth of the line will tell how fast the material is moving. If the lines shift back and forth we are able to learn that the star may be orbiting another star. We are able to estimate the mass and size of the star from this. If the lines grow and fade in strength we are able to find out about the physical changes within the star. Spectral data also can tell us concerning material around stars.