N.K. Chauhan 
Electromagnetic waves include different types of waves: visible light, ultraviolet, infrared rays, X-rays and gamma-rays etc.
Electromagnetic Spectrum is the classification of these waves according to their frequency.
The visible light from the sun is in between infrared (IR) and ultraviolet rays (UV) in the electromagnetic spectrum.
The emission or transmission of energy in the form of waves or particles through space or through a material medium is called radiation.
Wavelength is the distance between identical points (adjacent crests) in the adjacent cycles of a waveform signal.
Frequency and wavelength are inversely proportional to each other, twice the frequency means one-half the wavelength.
The wave with the greatest frequency has the shortest wavelength.
Electromagnetic radiation is a form of energy that is produced by oscillating electric and magnetic disturbance, or by the movement of electrically charged particles traveling through a vacuum or matter.
Electromagnetic spectrum
Electromagnetic spectrum is divided into seven regions, i.e. Radio waves, Microwaves, Infrared (IR) waves, Visible light, Ultraviolet (UV) rays, X rays and Gamma rays.
| Name | Frequency | Wavelength | Generation | Usage |
|---|---|---|---|---|
| Radio Waves | < 3 X 1011 Hz | > 1 mm | The accelerated motion of charges in conducting wires generates Radio waves. | AM, FM, TV and Cellular phones. |
| Microwaves | 3 X 1011 - 1013 Hz | 1 mm - 25 μm | Special vacuum tubes called klystrons, magnetrons and Gunn diodes generate microwaves. | Radar systems and Microwave ovens. |
| Infrared Rays (Heat Waves) |
1013 - 4 X 1014 Hz | 25 μm - 750 nm | Hot bodies and molecules generate Infrared rays. | Physical therapy, Earth Satellites and Remote switching of TV, video recorders, etc. |
| Visible Rays | 4 X 1014 - 7.5 X 1014 Hz | 750 nm - 400 nm | The Sun, Light Bulb etc. | |
| Ultraviolet Rays | 1015 - 1017 Hz |
400 nm - 1 nm | Welding arcs, special lamps and very hot bodies. The sun. |
LASIK eye surgery and Water purifiers. |
| X-rays | 1017 - 1020 Hz | 1 nm - 1 pm | X-rays are commonly generated by bombarding a metal target with high energy electrons. | As a diagnostic tool in medicine. |
| Gamma Rays | 1020 - 1024 Hz | < 10 -12 m | Gamma rays are produced in nuclear reactions. | Destroy cancer cells. |
The range of the AM (amplitude modulated) band is between 530 kHz and 1710 kHz.
TV waves range from 54 MHz to 890 MHz.
The FM (frequency modulated) radio band is from 88 MHz to 108 MHz.
Cellular phones also use radio waves to transmit voice communication in an ultra-high frequency (UHF) band.
Microwaves form the basis of microwave ovens. In microwave ovens, the frequency of the microwaves is selected to match the resonant frequency of water molecules.
This results in a direct transfer of energy from the waves to the kinetic energy of the water molecules raising the temperature of any food containing water.
Water molecules present in most materials readily absorb Infrared Rays.
After absorption, their thermal motion increases which increases their heat and that of their surroundings.
Ultraviolet Rays can have harmful effects on humans if exposed to in large quantities.
Ultraviolet Rays have shorter wavelengths.
Hence, they are focused into very narrow beams and used in high-precision applications like LASIK eye surgery.
Water purifiers use UV lamps to kill germs in water.
