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Electromagnetic Waves Important Points

Electromagnetic Spectrum

Name	Wavelength Range	Production	Uses
Gamma Rays	< 10-12 m	Gamma rays produced in radio active decay of nucleus	In treatment of cancer & to carry out nuclear reactions.
x-rays	10-9 m to 10-12 m	x-ray tubes or inner shell electrons	used as diagnostic tool in medical to find out fractures in bones & to find crack, flaws in metal part of machine
UV rays	4 × 10-7 to 10-9 m	By very hot bodies like sun and by UV lamps	In water purifier in detection of forged documents & in food preservation
Visible light	7 × 10-7 m to 4 × 10-7m	to by accelerated tiny (electrons) charge particles	to see every thing around us
IR rays	10-3 m to 4 × 10-7 m	due to vibration of atoms	in green houses to keep plant warm, to reveal secret writings on walls, in photography during fog and smoke
Microwaves	10-1 m to 10-3 m	produced in klystron Valve and magnetron Valve	In RADAR & in microwave ovens
Radio waves	> 0.1 m	by accelerated charged particles excited electrical circuits	In radio telecommunication system & in radio astrology

Electromagnetic Waves Important Points

• EM waves are produced by accelerated charged particles only if there is a change in speed; if the charged particle moves in a circular path without changing its speed, then there will be no electromagnetic wave produced by it where there is no change in speed.
• Electric field and magnetic field vectors oscillate with the frequency of oscillating charge particles.
• Properties of electromagnetic waves-
  • transverse in nature.
  • can travel through vacuum.
  • material not required for its propagation.
  • speed of EM wave v = E / B = E₀ / B₀
  • speed of EM waves in vacuum, c = 1 / √(μo єo) = 3 x 10⁸ m/s.
  • speed of EM waves in a medium, v = 1 / √(μ є)

• In an electromagnetic spectrum, different waves have different frequency and wavelengths.
• Penetration power of electromagnetic waves depends on frequency. Higher, the frequency larger the penetration power.

* Wavelength and frequency are related with each other . Here v is the wave velocity.

• A wave travelling along + x axis is represented by,

wave speed

Wave number

Displacement current (I_d) :

The Current which is produced due to time varying electric field or electric flux.

, is the electric flux.

Modified Ampere’s Circuital Law by Maxwell –

∮ ,

is the conduction current.

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