Electromagnetic Spectrum

The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from below one hertz to above 10²⁵ hertz, corresponding to wavelengths from thousands of kilometers down to a fraction of the size of an atomic nucleus. This frequency range is divided into separate bands, and the electromagnetic waves within each frequency band are called by different names; beginning at the low frequency (long wavelength) end of the spectrum these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays at the high-frequency (short wavelength) end. The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications. The limit for long wavelengths is the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length. Gamma rays, X-rays, and high ultraviolet are classified as ionizing radiation as their photons have enough energy to ionize atoms, causing chemical reactions.

 

What are Electromagnetic Spectrum?

The electromagnetic spectrum is a range of frequencies, wavelengths and photon energies covering frequencies from below 1 hertz to above 1025 Hz corresponding to wavelengths which are a few kilometers to a fraction of the size of an atomic nucleus in the spectrum of electromagnetic waves. Generally, in a vacuum electromagnetic waves tend to travel at speeds which is similar to that of light. However, they do so at a wide range of wavelengths, frequencies, and photon energies.

The electromagnetic spectrum consists of a span of all electromagnetic radiation which further contains many subranges which are commonly referred to as portions. These can be further classified as infra-red radiation, visible light or ultraviolet radiation.

                Electromagnetic Waves in Electromagnetic Spectrum

The entire range (electromagnetic spectrum) is given by radio waves, microwaves, infrared radiation, visible light, ultra-violet radiation, X-rays, gamma rays and cosmic rays in the increasing order of frequency and decreasing order of wavelength. The type of radiation and their frequency and wavelength ranges are as follows:

Type of Radiation	Frequency Range (Hz)	Wavelength Range
gamma-rays	1020 – 1024	< 10-12 m
x-rays	1017 – 1020	1 nm – 1 pm
ultraviolet	1015 – 1017	400 nm – 1 nm
visible	4 – 7.5*1014	750 nm – 400 nm
near-infrared	1*1014 – 4*1014	2.5 μm – 750 nm
infrared	1013 – 1014	25 μm – 2.5 μm
microwaves	3*1011 – 1013	1 mm – 25 μm
radio waves	< 3*1011	> 1 mm

The electromagnetic spectrum can be depicted as follows :

We see the uses of the electromagnetic waves in our daily life as :

Radio: A radio basically captures radio waves that are transmitted by radio stations. Radio waves can also be emitted by gases and stars in space. Radio waves are mainly used for TV/mobile communication.

Microwave: This type of radiation is found in microwaves and helps in cooking at home/office. It is also used by astronomers to determine and understand the structure of nearby galaxies and stars.

Infrared: It is used widely in night vision goggles. These devices can read and capture the infrared light emitted by our skin and objects with heat. In space, infrared light helps to map the interstellar dust.

X-ray: X-rays can be used in many instances. For example, a doctor can use an x-ray machine to take an image of our bone or teeth. Airport security personnel use it to see through and check bags. X-rays are also given out by hot gases in the universe.

Gamma-ray: It has a wide application in the medical field. Gamma-ray imaging is used to see inside our bodies. Interestingly, the universe is the biggest gamma-ray generator of all.

Ultraviolet: Sun is the main source of ultraviolet radiation. It causes skin tanning and burns. Hot materials that are in space also emit UV radiations.

Visible: Visible light can be detected by our eyes. Light bulbs, stars, etc. emit visible light.

Spectroscopy:

Spectroscopy is used to study the way different electromagnetic waves interact with the matter.

We can learn about a substance by analyzing the EM spectrum given by it. When light scatters or passes through matter, it tends to interact with the molecules and atoms. Since atoms and molecules have resonance frequencies they directly interact with those light waves having the exact frequencies. When collisions occur in an excited state, the atoms and molecules emit light with a certain set of characteristic frequencies. This further results in a line spectrum. Here, only light with detached wavelengths is produced. The spectrum is also not continuous but it consists of a set of emission lines.

In cases where the light with continuous wavelengths passes through a low-density material, the atoms and molecules of the material will absorb light waves with the same set of characteristic frequencies. This results in the production of the absorption spectrum which is a nearly continuous spectrum with missing lines.

Significance of Electromagnetic Spectrum

The electromagnetic waves in these different bands have different characteristics depending upon how they are produced, how they interact with matter and their practical applications. Maxwell’s equations predicted the existence of an infinite number of frequencies of electromagnetic waves, all travelling with the speed of light. This is the first indication of the existence of the entire electromagnetic spectrum.

Nonetheless, the main significance of the electromagnetic spectrum is that it can be used to classify electromagnetic waves and arrange them according to their different frequencies or wavelengths.

Practical Applications of Electromagnetic Waves

● The radio waves and microwaves discovered by Hertz paved the way for wireless television and radio and mobile communication.

● The visible light portion of the electromagnetic spectrum is the reason for all visual aids in daily life. This is the portion of the electromagnetic spectrum which helps us to see all the objects, including the colours.

● The X-rays discovered by Roentgen proved to be useful in medicine for detecting many ailments or deformities in bones.

● The high ultraviolet radiation has energies to ionize the atoms causing chemical reactions.

● The gamma rays discovered by Paul Villard are useful for ionization purposes, and for nuclear medicine.