mechanics and waves

8/7/2019 MECHANICS AND WAVES

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WHAT IS ELECTROMAGNETIC

WAVES????� Electromagnetic waves are formed when

there is a continuing process of an electric

field developing a magnetic field and vice

versa. An electromagnetic wave has both,

electric as well as magnetic components.

� The production of magnetism due to electric

current is known as electromagnetism.



ELECTROMAGNETIC WAVES

� Electromagnetic waves first formally

postulated by James Clerk Maxwell.

� James Clerk Maxwell derived a wave form of

the electric and magnetic equations, thus

uncovering the wave-like nature of electric

and magnetic fields, and their symmetry.



� Because the speed of EM waves predicted by

the wave equation coincided with the

measured speed of light, Maxwell concluded

that light itself is an EM wave.



� The discovery of electromagnetic waves

proved to be revolutionary as these waves

have various uses. Long, short, FM radio

waves, television and telephone signals can all

be transmitted through electromagnetic

waves. These waves also transmit energy in

the form of X-rays, gamma rays, UV rays andinfrared radiation.



Shows the relative wavelengths of

the electromagnetic waves of threedifferent colors of light (blue, green

and red) with a distance scale in

micrometers along the x-axis.



Wavelength of an electromagnetic

wave.



PROPERTIES OF EM WAVES

� Electromagnetic waves can be imagined as a

self-propagating transverse oscillating wave of

electric and magnetic fields.

This diagram shows a plane linearly polarized

wave propagating from right to left. The

electric field is in a vertical plane and the

magnetic field in a horizontal plane.



� Light travels through space in the form of

electromagnetic waves.

� The earth receives maximum amount of electromagnetic energy from the sun. This energy

reaches the earth through a vacuum.

� As the wavelength in the spectrum decreases, theamount of energy carried by the waves increase.This can be illustrated by the formula,E= hc/



� Electromagnetic waves can travel through

vacuum, i.e., they do not require a mediumfor transmission.

� Electromagnetic waves are two dimensional

transverse waves, i.e., the transfer of energy isperpendicular to the oscillations.

� All types of electromagnetic waves travel at

the speed of light and at the same speed invacuum.



� Electromagnetic waves have no mass.

� Velocity of electromagnetic wave is equal tothe speed of light, which is approximately

3×108 m/sec

�Electromagnetic waves follow the laws of reflection as well as refraction.

� The frequency of the waves remain same

when they change medium duringtransmission.



PARTICLE THEORY

� Energy of an EM interaction is quantized, so

EM waves are emitted and absorbed as

discrete packets of energy, or quanta, called

photons.

� Because photons are emitted and absorbed by

charged particles, they act as transporters of

energy, and are associated with waves withfrequency proportional to the energy carried.



� The energy per photon can be related to the

frequency via the PlanckEinstein equation:

Where:

E= Energy

h= Plancks constant

f= frequency



� The energy is commonly expressed in the unit of

electron volt (eV).

� This photon-energy expression is a particular case

of the energy levels of the more generalelectromagnetic oscillator, whose average energy,

which is used to obtain Planck's radiation law, can

be shown to differ sharply from that predicted by

the equipartition principle at low temperature,thereby establishes a failure of equipartition due

to quantum effects at low temperature.



DIELECTRIC CONSTANT OF A PLASMA

� A plasma is very similar to a gaseous medium,

expect that the electrons are free: i.e., there is

no restoring force due to nearby atomic

nuclei.

Plasma frequency



� For frequencies above the plasma frequency,

the dielectric constant of a plasma is less than

unity. Hence, the refractive index, is

also less than unity.

� This would seem to imply that high frequency

electromagnetic waves can propagate through

a plasma with a velocity which isgreater than the velocity of light in a vacuum.



� On the other hand, for frequencies below the

plasma frequency, the dielectric constant is

negative, which would seem to imply that the

refractive index is imaginary.



THANK YOU!!

mechanics and waves

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