There are many characteristics in which the most important are as given below.
( i ) Representation in the form of equations: With reference to the figure ( previous page ),
the radiated components of electric and magnetic field of the electromagnetic wave can
be represented by the equations,
E = [ E0 sin ( wt - kx ) ]^j and B = [ B0 sin ( wt - kx ) ]^k
( ii ) E and B are related by the equation, E / B = c ( velocity of light )
( iii ) Maxwell derived the equation for the velocity of electromagnetic wave in vacuum ( free
space) as
C = 1 / (U0 E0) where, U0 = 4 p * 10exp(- 7) N A- 2 is the permeability of free space and
E0 = 8.85 * 10exp(- 12) C 2 N - 1 m- 2 is the permittivity of free space.
Using these values of U0 and E0 , c = 2.98 * 10exp(8) m s- 1.
This value of c is equal to the velocity of light in vacuum indicating that light is also a
form of electromagnetic wave.
( iv ) Electromagnetic waves are transverse waves.
( v ) Electromagnetic waves possess energy.
( vi ) Electromagnetic waves exert pressure on a surface and impart linear momentum to it
when they are incident on it.
If U is the energy of electromagnetic waves incident on a surface of unit area per
second normal to it and is completely absorbed, then pressure exerted is given by p = u / c which is also the momentum of electromagnetic radiation transferred to it.
( vii ) Electromagnetic field prevails in the region where the electromagnetic waves propagate.
The electromagnetic energy per unit volume in the region ( energy density )
( viii ) “The intensity of radiation ( I ) is defined as the radiant energy passing through unit
area normal to the direction of propagation in one second.”
That is I = Energy / time / Area = Power / Area
As shown in the figure, the radiant energy passing through unit area
in one second is confined to a volume of length equal to c. If the energy density, then the energy in the above volume = density (c).
( ix ) In the region far away from the source, electric and magnetic fields oscillate in phase and are called radiated components of electromagnetic radiation.
( i ) Representation in the form of equations: With reference to the figure ( previous page ),
the radiated components of electric and magnetic field of the electromagnetic wave can
be represented by the equations,
E = [ E0 sin ( wt - kx ) ]^j and B = [ B0 sin ( wt - kx ) ]^k
( ii ) E and B are related by the equation, E / B = c ( velocity of light )
( iii ) Maxwell derived the equation for the velocity of electromagnetic wave in vacuum ( free
space) as
C = 1 / (U0 E0) where, U0 = 4 p * 10exp(- 7) N A- 2 is the permeability of free space and
E0 = 8.85 * 10exp(- 12) C 2 N - 1 m- 2 is the permittivity of free space.
Using these values of U0 and E0 , c = 2.98 * 10exp(8) m s- 1.
This value of c is equal to the velocity of light in vacuum indicating that light is also a
form of electromagnetic wave.
( iv ) Electromagnetic waves are transverse waves.
( v ) Electromagnetic waves possess energy.
( vi ) Electromagnetic waves exert pressure on a surface and impart linear momentum to it
when they are incident on it.
If U is the energy of electromagnetic waves incident on a surface of unit area per
second normal to it and is completely absorbed, then pressure exerted is given by p = u / c which is also the momentum of electromagnetic radiation transferred to it.
( vii ) Electromagnetic field prevails in the region where the electromagnetic waves propagate.
The electromagnetic energy per unit volume in the region ( energy density )
( viii ) “The intensity of radiation ( I ) is defined as the radiant energy passing through unitarea normal to the direction of propagation in one second.”
That is I = Energy / time / Area = Power / Area
As shown in the figure, the radiant energy passing through unit area
in one second is confined to a volume of length equal to c. If the energy density, then the energy in the above volume = density (c).
( ix ) In the region far away from the source, electric and magnetic fields oscillate in phase and are called radiated components of electromagnetic radiation.
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