Electromagnetic Spectrum
After the experimental discovery of electromagnetic waves by karts many other electromagnetic waves were discovered by different ways of excitation.
The orderly distribution of electromagnetic radiations according to their wavelength or frequency is called the electromagnetic spectrum.
The electromagnetic spectrum has much wider range with wavelength variation 10-14 to 6 X 102m. The whole electromagnetic spectrum has been classified into different parts and subparts in order of increasing wavelength according to their type of excitations. There is overlapping in certain parts of the spectrum showing that the methods. It may be noted that the physical properties of electromagnetic waves are decided by their wavelengths and not by the method of their excitation.
Only a small part of the complete electromagnetic spectrum is visible to human eye, as the radiations of this part can produce some sensation on the retina of the eye. This part of the spectrum s called visible spectrum the radiations of different wavelengths in the visible part of the spectrum produces different colours on the retina of our eye. This is given in the following table.
| λ (m) X 10-7 |
Colour |
λ (m) X 10-7 |
Colour |
| 4 to 4.5 |
Violet/indigo |
5.7 to 5.9 |
Yellow |
| 4.5 to 5.0 |
Blue |
5.9 to 6.2 |
Orange |
| 5.0 to 5.7 |
Green |
6.2 to 7.8 |
Red |
Tables given below shows the various parts of the electromagnetic spectrum with approximate wavelength range frequency range their sources of production and detections.
| Type |
Wavelength range (m) |
Frequency range (Hz) |
Production |
Detection |
| Radio waves |
0.3 to 6 X 102 |
109 to 5 X 105 |
Oscillating circuit or rapid acceleration and retardation of electrons in aerials |
Receivers aerials |
| Micro wave |
10-3 to 0.3 |
3 x 1011 to 1 x 109 |
Klystron value of magnetron value |
Point contact diodes |
| Infrared |
8 x 10-7 to 1 x 10-3 |
4 x 1014 to 3 x 1011 |
Vibrations of atoms and molecules |
Thermopile bolometer infrared photographic films |
| Visible light |
4 X 10- 7 to 8 x 10-7 |
8 x 1014 to 4 x 1014 |
Excitation of valency electr4ons in atoms |
Human eye photo cells photographic plate |
| Ultra violet |
6 x 10-10 to 4 x 10-7 |
5 x 1017 to 8 x 1014 |
Excitation of atoms spark and are lamps |
Photo cells photographic film |
| X-rays |
1 x 10-13 to 3 x 10-8 |
3 x 1021 to 1 x 1016 |
X - ray tubes or excitation of inner shell electron |
Photographic film Geiger tubes |
| Gamma rays |
0.6 x 10-14to 1 x 10-10 |
5 x 1022 to 3 x 1018 |
Nuclear origin |
Photographic film lionization chamber |
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