Electromagnetic Spectrum

Electromagnetic Spectrum

The orderly distribution of electromagnetic radiations according to their wavelength or frequency as called the electromagnetic spectrum. Electromagnetic spectrum has a very wide range with wavelength variation from 10^-13m to 6×10⁶m.

The usual classification of the electromagnetic spectrum is explained below

1. Radio waves

   These are electromagnetic waves of the frequency range from few Hz to 10⁶ Hz.These waves, which are used in television and radio broadcasting systems, are generated by electronic devices, mainly oscillating circuits having an inductor and capacitor.
   
   

2. Microwaves

   The wavelength of microwaves is greater than 1.0 mm and less than 30 cm. The frequency range of microwaves is 10⁹Hz to 3.0×10¹¹Hz.They are produced by oscillating electrons in a cavity. The commonly used oscillators to produce microwaves are Klystron and Magnetron.
   
   Uses of Microwaves

• Microwaves are used in a radar communication.
• These are used for atomic and molecular research.
• These are used for aircraft navigation.
• These are used in microwave ovens for cooking and warming food.

3. Infra-red (IR) rays

   The wavelength range of infra-red rays 1 nm to 700 nm and the frequency range is 3.0 × 20¹¹Hz to 4.3 × 10¹⁴Hz Infrared rays are produced by the excitation of atoms and molecules. Hot bodies also radiate infra-red rays.
   
   Uses of Infra-red Rays

• These rays can pass through the haze, fog, and mist, so these are used in night vision devices during warfare and for taking photographs of the earth under foggy conditions from a great height.
• These rays are used to keep the greenhouse warm.
• They are used in revealing the secret writings on the ancient walls.
• They are used to treat muscular strains.
• The infra-red rays from the sun keep the earth warm.
  
  

4. Visible Light

   The range of visible light is 400 nm to 60 nm and their frequency range is 4.3×10¹⁴Hz to 7.5×10¹⁴Hz.Visible light is emitted when an electron jumps from higher energy level to lower energy level of an atom.
   
   Uses of Visible Light

• Visible light stimulates the sense of sight so we can see the beautiful world in the presence of visible light.
• Visible light is useful in photography.
• It is useful in optical microscopy and
• It is useful astronomy.
  
  

5. Ultra-violet (UV) rays

   The range of ultra-violet rays is 400 nm to 60 nm and their frequency range is 7.5×10¹⁴Hz to 5×10¹⁵Hz.The sun is the most important source of ultra-violet rays. Ultra-violet rays are produced by the spark of welding. These rays are harmful to the living tissues.
   
   Uses of Ultra Violet Rays

• They are used to preserve food stuff and make drinking water free from bacteria as these rays can kill bacteria, germs etc.
• They are used for sterilizing the surgical instruments.
• They are used in detecting the invisible writings, forged documents, and finger prints.
• They are used to study the structure of molecules.

6. X-rays

   X-rays can be produced by bombarding a target of high atomic number (Z) with a beam of fast-moving electrons. The range of the wavelength of X-rays varies from 60 nm to 10^-8.The frequency of these waves varies from 5.0×0¹⁵Hz to 3.0×10¹⁸Hz. X-rays can penetrate through the human flesh, but bones or metallic materials block these days.
   
   Uses of X-rays

• These are used in medical diagnosis like locating the fracture in the bone, foreign materials, like coin or bullet in the body.
• These are used in radiotherapy to cure skin diseases, cancer, and tumors.
• These are used in engineering for locating the faults, cracks, and flaws in the finished metallic materials.
• X-rays are used by detective agencies to detect gold, silver, diamonds and other contraband goods etc. concealed in bags or the body of a person.

7. Gamma rays

   γ-rays are produced during radioactive decay of nuclei and nuclear reactions. The wavelength of γ-rays is the shortest of all the electromagnetic waves. The range of the wavelength of these rays varies from 1.0 nm to 10^-5On the other hand, the frequency of γ-rays in the highest of all the electromagnetic waves. The range of the frequency of γ-rays is between 3.0¹⁸Hz to 3.0×10²² Hz.
   
   Uses of γ-ray

• In the treatment of cancer and tumors.
• To pressure the foodstuffs for a long time as the soft γ-rays can kill microorganisms easily.
• To produce nuclear reactions.
• To provide valuable information about the structure of the atomic nucleus.

References

Manu Kumar Khatry, Manoj Kumar Thapa, Bhesha Raj Adhikari, Arjun Kumar Gautam, Parashu Ram Poudel. Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.

S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.