Spectrum: Definition, Classification and Applications

Spectrum: What is Spectrum? A Spectrum is a range of band of colours that appear when light passes through a prism or water drops. The best example of a Spectrum is  a rainbow. Rainbows are multicoloured arcs made by light passing the water droplets. Rainbow appears as a spectra of various colours: violet, indigo, blue, green, yellow, orange and red. 

Have you ever noticed how violet merges with blue, blue to green? In a rainbow, sunlight travels through raindrops and is scattered to produce various colours. You can also see a small rainbow if you just hold a transparent plastic scale against the sunlight. What you see on the scale is a portion of the electromagnetic radiation called the Spectrum.

Spectrum: Definition

The spectrum is a continuous range of electromagnetic radiation waves. 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, tag our friends on Instagram, call an Uber, pull up directions to a destination, and do everything on our mobile devices. The frequencies we use for wireless communication are only a portion of what is called the electromagnetic spectrum.

Mobile phones, TV remotes, and similar gadgets respond to our demands instantly when we press a few buttons, thanks to the invisible electromagnetic waves that these devices emit or receive. The technologies that make wireless networks work can be hard to visualize, we’ve even called them magical. In this article we will be discussing the lifeblood of wireless networks: Spectrum, and the new ways to harness its power.

What Is the Spectrum of Light?

The band of colours obtained on a screen on passing white light through a prism is called the spectrum. The prism has split the incident white light into a band of colours. The splitting of white light takes place due to refraction. As light travels from a denser medium to a rarer medium, it splits up into a band of colours This happens because white light is composed of lights of different colours having different wavelengths and frequencies.

The splitting of white light takes place due to refraction. As light travels from a denser medium to a rarer medium, it splits up into a band of colours This happens so because white light is composed of lights of different colours having different wavelengths and frequencies.

What Is an Electromagnetic Spectrum?

The electromagnetic (EM) spectrum is the range of all types of EM radiation. Radiation is the energy given off by matter in the form of rays or high-speed particles. The visible light that comes from a lamp to the rays used to figure out a fractured bone, all are forms of electromagnetic radiation. And the series of these different radiations is called the electromagnetic spectrum.

The entire electromagnetic spectrum encompasses other frequencies we interact with daily, even if we do not think about them. These are microwaves, infrared light, ultraviolet light, X-rays, and gamma-rays. You may remember VIBGYOR from elementary school. That is the acronym for the colours that make up the visible part of the electromagnetic spectrum—the spectrum we see. Portions of the electromagnetic spectrum are grouped in “bands” depending on their wavelengths—the distance over which the wave’s shape repeats. The full electromagnetic spectrum ranges from \({\rm{3\; \times \;1}}{{\rm{0}}^{{\rm{21}}}}{\rm{\;Hz}}\) (extremely low frequency) to 300 kHz (gamma rays).

What Are the Different Types of Spectrum?

Depending on the ability of a substance to emit or absorb white light, Spectrum can be broadly classified into the following two categories:

Emission Spectra

The spectrum obtained by the radiation emitted by a substance that has absorbed energy is called emission spectra. The electrons in an atom always acquire a stable energy state. This stable energy state called the ground state of an atom is the lowest energy state of the atom. Atoms, molecules, or ions get ‘excited’ about absorbing radiation. When it returns to the ground state, it releases the energy that it had previously gained often in the form of electromagnetic radiation. To produce emission spectra, the wavelength or the frequency of the radiation is recorded, when the sample under examination gives up the absorbed energy.

1. Energy is absorbed when an electron passes from a lower energy level to a higher energy level. This means a specific wavelength is absorbed. Consequently, a dark line will appear in the spectrum which constitutes the absorption spectrum.
2. Energy is released when an electron passes from a higher to a lower energy level. This means a spectral line of wavelength is emitted. This line constitutes the emission spectrum. There are two types of these.

(a) Continuous Spectrum (Thermal or Black body spectra): Remember, a rainbow is a continuous spectrum of the seven colours beautifully merging into one another. Dense gases or solid objects when radiate heat, this spectrum is formed. They emit radiation over a broad range of wavelengths; thus the spectra appear smooth and continuous.

(b) Discontinuous Spectrum: A discontinuous electromagnetic spectrum is the 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 can be categorized into the following.

Line Spectra or Atomic Spectra

An electron in the excited state when makes the transition to lower energy states, the light of certain fixed wavelengths is emitted. These emitted wavelengths appear as sharp bright lines in the dark background forming a spectrum. This is known as the line emission or discontinuous spectrum. As electrons are part of the atom, Line spectra are also called atomic spectra Inert gases, metal vapors, and atomized non-metals form this kind of spectra. The atomic spectrum of the elements is a “characteristic property” of the elements and is often termed as “fingerprints” of the elements.

Band Spectra or Molecular Spectra

This spectrum is given by hot metals and molecular non-metals. In this type of spectra discontinuity or gaps appear between the bands or closely spaced bright lines. It is 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 given range whereas the line spectrum contains only a few wavelengths.

Absorption Spectrum

It is formed by electromagnetic radiation that has passed through a medium in which radiation of certain frequencies is absorbed. In an absorption spectrum, portions of a continuous spectrum appear as dark lines or gaps. These dark lines indicate that the wavelengths have been absorbed by the medium through which the light has passed. An absorption spectrum shows us which wavelengths from light were absorbed by a particular gas. It looks like a continuous spectrum, or rainbow, with some black lines.

Difference between Emission, Continuous, and Absorption Spectrum

What is Hydrogen Spectrum?

Hydrogen gas radiates when subjected to electric discharge in a discharge tube under low pressure. The radiation emitted by the hydrogen atom is analyzed with the help of a spectrograph. It is found to consist of a series of sharp lines in the UV, visible, and IR regions. This series of lines is known as the line or atomic spectrum of hydrogen. The lines in the visible region can be directly seen on the photographic film.

The hydrogen spectrum consisting of series of lines that corresponds to light of a definite wavelength. The entire spectrum consists of six series of lines. Each series of lines is known after its discovery as the Lyman, Balmer, Paschen, Brackett, Pfund, and Humphrey series. The wavelength of all these series can be expressed by a single formula, which is attributed to Rydberg.
\(\frac{{\rm{1}}}{{\rm{\lambda }}}{\rm{ = k = R\;}}\left( {\frac{{\rm{1}}}{{{\rm{n}}_{\rm{1}}^{\rm{2}}}}{\rm{ – \;}}\frac{{\rm{1}}}{{{\rm{n}}_{\rm{2}}^{\rm{2}}}}} \right){\rm{\;}}\)
Where \(k\; = \) wave number;
\({\rm{\lambda }}\) = wavelength;
\(R\; = \) Rydberg constant \(\left( {{\rm{109677\;c}}{{\rm{m}}^{{\rm{ – 1}}}}} \right)\) \({{\rm{n}}_{\rm{1}}}{\rm{,\;}}{{\rm{n}}_{\rm{2}}}{\rm{\;are\;the\;energy\;levels}}\)

According to Bohr’s theory, an excited electron is quite unstable and will release energy in the form of photons in order to return to its ground state.
The experimental values and the frequencies of the spectral lines calculated with the help of the above equation are found to be in good agreement. Thus, Bohr’s theory elegantly explains the line spectrum of hydrogen and hydrogen-like species.

What Is Spectrum in Telecommunication?

The world has become a “global village”, thanks to cell phones. With just one click we can chat, call and see people miles apart. But how are these mini gadgets able to connect us with people distances thousands of kilometers apart? These mini gadgets make use of invisible electromagnetic radiation. Whenever we use our phones, either for internet use or making a voice call, we send or receive invisible electromagnetic waves. These waves are picked up by our cell towers transmitted towards the destination tower and finally to the end-user.

Applications of Spectrum

Electromagnetic Spectrum

1. Gamma rays – These rays are used to sanitize medical equipment and inhibit the growth of micro-organisms.
2. X-rays – These ays are used to visualize the inside of a body without making an incision. These rays are used for scanning purposes.
3. Ultraviolet light – These rays kill microbes, hence is used extensively to disinfect equipment.
4. Visible light – These rays help us to see things around us.
5. Infrared rays – As these rays can easily penetrate the skin, are used widely in cosmetic applications. It is 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. Also used to guide airplanes.
7. Radio waves are used in radio and TV broadcasts.

Emission and Absorption Spectroscopy

1. Determining the atomic structure of a sample
2. Determining the metabolic structure of a muscle
3. Monitoring dissolved oxygen content in freshwater and marine ecosystems
4. Studying spectral emission lines of distant galaxies
5. Altering the structure of drugs to improve effectiveness.
6. Characterization of proteins.
7. Space exploration.
8. Respiratory gas analysis in hospitals.

Spectrum Meaning : Summary

From this article, we can conclude that we are continuously under the effect of electromagnetic radiation. From warming ourselves under the Sun during winter to tuning our radio, to watching TV, sending a text message, or popping popcorn in a microwave oven, we are using electromagnetic energy. We depend on this energy every hour of every day. Without it, the world we know could not exist at all.

Frequently Asked Questions About Spectrum

Let’s look at some of the commonly asked questions about Spectrum:

Q1. What is the connection between emission and absorption spectrum?
Ans. Emission lines refer to the radiation emitted by a glowing hot gas, whereas absorption lines are obtained when cool atmospheric gas absorbs the same lines of light. When light passes through the gas in the atmosphere some of the light at particular wavelengths is scattered resulting in darker bands.

Q2. Why don’t NASA and other space programs use gamma rays, and not radio waves to transfer signals?
Ans. Gamma rays can easily pass through clouds and are not blocked by clouds. Since radio waves have less energy than gamma rays, it’s more likely for radio waves to be blocked by clouds.

Q3. A good absorber is also a good emitter: True or False?
Ans. True. Dark matter substances are good at both emitting and absorbing radiation.

Q4. What 2 properties are common to all types of electromagnetic radiation?
Ans. 1. They travel at the speed of light.
2. They can travel across a vacuum.

Q5. What is meant by Spectrum in physics and chemistry?
Ans. Whether it is physics or chemistry, the meaning of spectrum remains the same. It is the band of colours obtained on a screen when white light is allowed to pass through a prism.

Q6. Which type of electromagnetic radiation radiates from warm objects?
Ans. Infrared.

PRACTICE QUESTIONS ON SPECTRUM

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