In electromagnetic radiation, if we draw an oscillating electric field in the plane of the page the magnetic field will be perpendicular to it. One will be in X-axis whereas another will be in Y-axis on the paper. The interaction of electromagnetic radiation with different atoms and molecules helps to predict the structure of molecules.
Amplitude, wavelength, and frequency are some basic properties of electromagnetic radiations. When wave in a certain direction, it makes trough and crest. Here troughs are the lowest points and crests are the highest points. The distance between the tip of a crest and the wave’s central axis is called amplitude of the wave. The amplitude of a wave is associated with the intensity of the wave. The wavelength can be defined as the distance between two consecutive troughs or crests.
Different types of electromagnetic radiation can be arranged according to their wavelength and frequency values. This ordered arrangement of electromagnetic radiation is called the electromagnetic spectrum.
The leftmost part is with electromagnetic radiations with the lowest value of wavelength and highest frequency. Since the energy of radiation is directly proportional to frequency therefore as the frequency increases, the energy of electromagnetic radiation also increases. Gamma rays are the most energetic radiations whereas radio waves have the least energy values. The decreasing order of energy for electromagnetic radiations is given below.
Gamma rays ⇒ X-rays ⇒ UV radiations ⇒ Visible rays ⇒ Infrared rays ⇒ microwaves ⇒ Radio waves
The visible part of the electromagnetic spectrum is also called as a colour spectrum as it consists of seven colours which are arranged from higher energy to lower energy values. Visible colour light is located in the middle of the spectrum. It comprises a very small fraction of the overall electromagnetic spectrum.
The visible colour spectrum lies between the ultraviolet and infrared region of the electromagnetic spectrum. Due to the low energy of infrared (IR) rays, microwaves, and radio waves, they are not harmful to living ones. On the contrary, ultraviolet, gamma rays, cosmic rays, X-rays are with high energy and frequency that make them harmful for living ones.
The Sun is the most common source of ultraviolet radiation. Our eyes have some special living cells which are sensitive to visible light that lies from a wavelength range of 400 – 700 nanometers (nm). We cannot see the radiations which have wavelength shorter or longer than visible light.
That is the reason; this region of the electromagnetic spectrum is called a visible spectrum or colour spectrum. It consists of 7 colour mainly; violet, blue, green, yellow, orange, and red. Violet colour has the shortest wavelength and red has the longest wavelength value. The mixture of all the colours of the visible colour spectrum forms white light whereas black is due to the absence of light.
The colours of the visible colour spectrum from higher energy to lower energy are listed below.
The violet colour has a wavelength of about 400 nm and located at the leftmost corner of the visible colour spectrum. In the colour spectrum, violet and blue wavelengths are scattered more efficiently compared to other colours. Next colour is indigo that has wavelength value of 445 nm. Next is blue light that has a wavelength of about 475 nm.
Due to shorter wavelength, blue light is scattered more efficiently in the atmosphere. That causes the blue colour of the sky. After the blue colour, there is a green colour at a wavelength value of 510 nm. Objects like grass appear green because they can absorb all of the colours in the visible part except green. So green light is reflected and grass appears green.
After green light, yellow light is present in the visible colour spectrum at 570 nm of wavelength. The visible region at 590 nm is associated with orange color. Objects like low-pressure sodium lamps emit orange light and appear the same colour. The colour with the longest wavelength at about 650 nm is associated with red colour.
Different colours of colour spectrum with their wavelength, frequency and energy values are listed below.
|Colour spectrum wavelength, frequency and energy values|
|Violet||380–450 nm||668–789 THz 2.75–3.26 eV|
|Blue||450–495 nm||606–668 THz 2.50–2.75 eV|
|Green||495–570 nm||526–606 THz 2.17–2.50 eV|
|Yellow||570–590 nm||508–526 THz 2.10–2.17 eV|
|Orange||590–620 nm||484–508 THz 2.00–2.10 eV|
|Red||620–750 nm||400–484 THz 1.65–2.00 eV|
The colour light that human eyes cannot detect or absorb cannot be seen by humans. Like we cannot see ultraviolet and IR radiation as our eyes cannot detect them.