RFUnderstanding the Electromagnetic Spectrum
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All electromagnetic waves travel at the same velocity (3 x 10^8 m/s) in free space, but they differ in frequency. The arrangement of electromagnetic radiations according to their wavelength or frequency is known as the electromagnetic spectrum. This spectrum doesn’t have a definite upper or lower limit, and the boundaries between different regions aren’t sharply defined.
The table below outlines the types of electromagnetic waves, their frequencies, wavelengths, sources, and applications. As mentioned, EM waves include electric waves, radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays, and cosmic rays.
| EM wave type | Frequency (Hz) | Wavelength (m) | Source | Applications |
|---|---|---|---|---|
| Electric Wave | 50 to 60 | 5 x 10^6 to 6 x 10^6 | Weak radiation from AC circuit | Lighting |
| Radio Wave | 3 x 10^4 to 3 x 10^9 | 1 x 10^-1 to 10^4 | Oscillating circuits | Radio communication, television |
| Microwave | 3 x 10^8 to 3 x 10^11 | 1 x 10^-3 to 1 | Oscillating currents in special vacuum tubes, Gunn, IMPATT, Tunnel diodes | Radar, TV, Satellite communication, remote sensing |
| Infrared | 1 x 10^13 to 4 x 10^14 | 7.5 x 10^-7 to 3 x 10^-5 | Excitation of atoms and molecules | Gives information on the structure of molecules and of external atomic electron shells, remote sensing |
| Visible light | 4 x 10^14 to 8 x 10^14 | 3.75 x 10^-7 to 7.5 x 10^-7 | Excitation of atoms and vacuum spark | Gives information on the structure of molecules and of external atomic electron shells, remote sensing |
| Ultra violet | 8 x 10^14 to 1 x 10^16 | 3 x 10^-8 to 3.75 x 10^-7 | Excitation of atoms and vacuum spark | Gives information on the structure of molecules and of external atomic electron shells, remote sensing |
| X-ray | 1 x 10^16 to 3 x 10^19 | 1 x 10^-10 to 3 x 10^-8 | Bombardment of high atomic number target by electrons | X-ray therapy, industrial radiography, medical radiography, crystallography |
| Gamma Ray | 3 x 10^19 to 5 x 10^20 | 6 x 10^-15 to 1 x 10^-10 | Emitted by radioactive substances | Gives information about the structure of atomic nuclei |
| Cosmic Ray | > 10^20 | < 10^-11 | Stars from other galaxies |
Figure 1 depicts the electromagnetic spectrum, showcasing various waves as described in the table above.
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