Top Concepts
1. Displacement current is due to time-varying electric field and is given
by
E
do
d
idt
Displacement current acts as a source of magnetic field in exactly the
same way as conduction current.
2. Electromagnetic waves are produced only by charges that are
accelerating, since acceleration is absolute, and not a relative
phenomenon. An electric charge oscillating harmonically with frequency ,
produces electromagnetic waves of the same frequency .
An electric dipole is a basic source of electromagnetic waves.
3. Electromagnetic waves with wavelength of the order of a few metres
were first produced and detected in the laboratory by Hertz in 1887. He
thus verified a basic prediction of Maxwell’s equations.
4. Electric and magnetic fields oscillate sinusoidally in space and time in
an electromagnetic wave. The oscillating electric and magnetic fields, E
and B are perpendicular to each other, and to the direction of propagation
of the electromagnetic wave.
5. For a wave of frequency , wavelength , propagating along z-direction,
we have
xo
oo
yo
oo
E E (t) E sin(kz t)
z z t
E sin 2 t E sin 2 T
B B (t) B sin(kz t)
z z t
B sin 2 t B sin 2 T
They are related by Eo/Bo=c
6. The speed c of electromagnetic wave in vacuum is related to 0 and 0
(the free space permeability and permittivity constants) as follows:
oo
c 1/
The value of c equals the speed of light obtained from optical
measurements. Light is an electromagnetic wave; c is, therefore, also the
speed of light. Electromagnetic waves other than light also have the same
velocity c in free space.
The speed of light, or of electromagnetic waves in a material medium is
given by
v 1/
where is the permeability of the medium and its permittivity.
1
1
1
1
1
u
Important Terms, Definitions & Formulae
By Mir Mohammed Abbas II PCMB 'A'
CHAPTER FORMULAS & NOTES
Formulae For ELECTROMAGNETIC WAVES
