MK Fisika Dasar 2_Bab14

7/23/2019 MK Fisika Dasar 2_Bab14

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MK FISIKA DASAR 2ENGE600004

4 SKS

Rachmat Andika

Multiferroic Research Group

Departemen FisikaFMIPA - UI



ELECTROMAGNETIC WAVES

POLARIZATION OF LIGHT



MATERI

Maxwell’s equations and Electromagnetic Waves

Plane Electromagnetic Waves

Energy Carried by Electromagnetic Waves

Momentum and Radiation PressureThe Natural Properties of Polarized light

Polarization by Absorption

Polarization by Reflection

Birefringent Polarization

Polarization by Scattering



MAXWELL’S EQUATIONS

Maxwell showed that electromagnetic waves are a natural

consequence of the fundamental laws expressed in thefollowing four equations

Maxwell, electromagnetic Newton, mechanical

Fundamental Law

Gauss’s Law

Gauss’s Law in magnetism

Faraday’s Law

Ampere-Maxwell Law



Schematic diagram of Hertz’s

apparatus

Hertz demonstrated:

Sparks were induced across the gap ofthe receiving electrodes when the

frequency of the receiver was adjusted

to match that of the transmitter

Oscillating current induced in thereceiver was produced by

electromagnetic waves radiated by the

transmitter



PLANE ELECTROMAGNETIC WAVES

The properties of electromagnetic waves can be deduced from

Maxwell’s equations.

If we define aray as the line along which the wave travels,

the all rays are parallel. This is called aPlane Wave

A surface connecting points of equal phase on all waves iscalled as awave front

Linearly

polarized waves



PLANE ELECTROMAGNETIC WAVES

Because this speed is precisely the same as the speed of

light in empty space, that light is an electromagnetic wave



At every instant the ratio of the magnitude of the electric

field to the magnitude of the magnetic field in anelectromagnetic waves equals the speed of light



LET US SUMMARIZE THE

PROPERTIES OF


The solutions of Maxwell’s third and fourth equations are

wave-like, with both E and B satisfying a wave equation

Electromagnetic waves travel through empty space at the

speed of light

The component of the electric and magnetic fields of plane

electromagnetic waves are perpendicular to each other and

perpendicular to the direction of wave propagation.

The magnitudes of E and B in empty space are related by the

expression E/B = c

Electromagnetic waves obey the principle of superposition



EXAMPLE 1

A sinusoidal electromagnetic wave of frequency 40.0 MHz

travels in free space in the x direction Determine the wavelength and period of the wave

At some point at some instant, the electric field has its maximum

value of 750 N/C and is along the y axis. Calculate the magnitude

and direction of the magnetic field at this position and time Write expressions for the space-time variation of the components

of the electric and magnetic fields for this wave



Determine the wavelength and period of the wave

At some point at some instant, the electric field has its maximum

value of 750 N/C and is along the y axis. Calculate the magnitude

and direction of the magnetic field at this position and time

Write expressions for the space-time variation of the components

of the electric and magnetic fields for this wave



ENERGY CARRIED BY


Electromagnetic waves carry energy and transfer energy

while they propagate through space

The rate of flow energy in an electromagnetic wave is

described by a vector S, called thePoynting Vector

the magnitude of theSrepresents power per unit area.

The direction of the vector is along the direction of wave

propagation SI units : J/s m2 = W/m2.



ENERGY CARRIED BY


The greater interest for sinusoidal plane electromagnetic

wave is the time average ofS over one or more cycles : Wave

Intensity (I)

The energy densityu E associated with an electric field or

energy densityu B associated with a magnetic field are

Both energy density are equals



ENERGY CARRIED BY


Electromagnetic wave Electric field

Magnetic field

Total energy per volume unit of the system that contains ofelectric field and magnetic field is

The mechanism of energy transfer from one

point to another point

The intensity of an electromagnetic wave equals the averagedensity multiplied by the speed of light



MOMENTUM

Electromagnetic waves transport linear momentum as well

as energy

When the momentum is absorbed by some surface,

pressure is exerted on the surface

The pressure exerted on the surface is defined as force per

unit area F/A.

If the surface is a perfect reflector and the momentum

transported to the surface in a time interval is twice.

Momentum transported to a perfectlyabsorbing surface

Radiation pressure exerted on a

perfectly absorbing surface

Radiation pressure exerted on a

perfectly reflecting surface



EXAMPLE 2

Many people giving presentations use a laser pointer

to direct the attention of the audience to information

on a screen. If a 3.0 mW pointer creates a spot on a

screen that is 2.0 mm in diameter, determine the

radiation pressure on a screen that reflects 70% of thelight that strikes it. The power 3.0 mW is a time-

averaged value.



EXAMPLE3

The Sun delivers about 103 W/m2 of energy to theEarth’s surface via electromagnetic radiation. Calculate the total power that is incident on a roof of

dimensions 8.00 m x 20.0 m

Determine the radiation pressure and the radiation force

exerted on the roof, assuming that the roof covering is a

perfect absorber



THE SPECTRUM OF


All forms of the various

types of radiation are

produced by the same

phenomenon –

accelerating charges



POLARIZATION OF LIGHT



CLASSIFICATION OF POLARIZATION

Light in the form of a plane wave in space is said to be

linearly polarized.

Light is a transverse wave, but natural light is

generally unpolarized.




Linear Polarization A plane electromagnetic wave is said to be linearly

polarized. The transverse electric field wave is

accompanied by a magnetic field wave




Circular PolarizationThe light consists of two perpendicular

electromagnetic plane waves of equal amplitude and

90o difference in phase.




Elliptical PolarizationThe light consists of two perpendicular waves of

unequal amplitude which differ in phase by 90o.



POLARIZATION BY SELECTIVE

ABSORPTION

The most common technique for producing polarized light To use a material that transmits waves whose electric fields vibrate in a

plane parallel to a certain direction and that absorbs waves whose electric

fields vibrate in all other directions.

IDEAL polarizer, all light with E parallel to the transmission axis

is transmitted, and all light with E perpendicular to thetransmission axis is absorbed



Malus’s law, applies to any two polarizing materials whose

transmission axes are at an angle to each other

Transmission axes are parallel, the intensity of the transmittedbeam is maximum

Transmission axes are perpendicular, the intensity is zero

(complete absorption by the analyzer)



POLARIZATION BY REFLECTION

When an unpolarized light beam is reflected from a surface, the

reflected light may be completely polarized, partially polarized, or

unpolarized, depending on the angle of incidence.

Polarizing angle

Brewster’s angle

MK Fisika Dasar 2_Bab14

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