________________
56. (a)
(4) In free space, electromagnetic waves travel with a velocity,
1
C=1= 3 x 108 m s1
άμε
i.e. with a velocity equal to that of light in free space.
In a material medium, velocity of electromagnetic waves is given by
1
V= νμε
where m and e are aboslute permeability and absolute permittivity of that medium.
(5) The electromagnetic waves obey he principle of superposition.
(6) The variations in the amplitudes of electric and magnetic fields in the electromagnetic waves always take place at the same time and at the same point in the space. Thus, the ratio of the amplitudes of electric and magnetic fields is always constant and it is equal to velocity of the electromagnetic waves. Mathematically,
E
B
(7) The energy in electromagnetic waves is divided equally between the electric and magnetic field vectors.
=C
(8) The electric vector is responsible for optical effects due to an electromagnetic wave. For this reason, electric vector is called light vector.
Text-book of Physics (Part II), p. 100The Electromagnetic Spectrum
After successful generation of electromagnetic waves by Hertz, scientists were convinced of the reality of electromagnetic waves, thus a study of the electromagnetic waves of different wavelengths began.
The X rays discovered by Rontgen in 1898 were shown to be electromagnetic waves in 1906. Subsequently, the spectrum of electromagnetic waves has bee studied over a range of wavelengths covering 10 meter on the short wave side to around 10 meter on the long wave side. The electromagnetic radiation is continuously distributed over the entire region. Our vision is
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