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Wave nature of Electromagnetic Radiations

 Wave nature of Electromagnetic Radiations


Maxwell , in 1873 , showed theoretically that an oscillating electrical circuit should radiate electromagnetic waves propagating with the velocity of light. 


The main features of this theory are :

1. Energy may be emitted from any source such as heated rod or filament of a bulb through which electric current is passed. Energy is emitted continuously in the form of radiations (waves). 

2. These waves are associated with oscillating electric field and magnetic field. These two fields are perpendicular to each other and perpendicular to the direction of propagation of the radiation as shown in the figure. 


Fig: Oscillating electric and magnetic fields emitted by charged particles. 


3. The radiations possess wave nature. Their velocity is equal to the velocity of light, i.e, 3×10⁸ m/sec. The radiations are called electromagnetic radiations or electromagnetic waves. 

4. Electromagnetic waves do not require any material medium for propagation. This rays of sun reach us through space. Space does not have material medium. But sound waves require medium and can not move in vacuum. 


Summary:

This suggested that light consisted of electromagnetic waves of extremely short wavelength. Fifteen years later, Hertz succeeded in producing short -wavelength waves of electromagnetic origin and showed that they possessed all the properties of light waves, such as reflection, refraction, polarization, etc. Thus Maxwell's electromagnetic theory of light was experimentally justified. 


Limitations of Electromagnetic Wave Theory

Electromagnetic wave theory explains the properties of light such as interference and diffraction etc. But this theory could not explain the following facts :

1. The phenomenon of black body radiation. 

2. The line spectra of atoms with special reference to hydrogen. 

3. The photoelectric effect. 

4. Variation of heat capacity of solids as a function of temperature. 


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