MK Fisika Dasar 2_Bab14
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Transcript of MK Fisika Dasar 2_Bab14
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MK FISIKA DASAR 2ENGE600004
4 SKS
Rachmat Andika
Multiferroic Research Group
Departemen FisikaFMIPA - UI
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ELECTROMAGNETIC WAVES
POLARIZATION OF LIGHT
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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
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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
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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
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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
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PLANE ELECTROMAGNETIC WAVES
Because this speed is precisely the same as the speed of
light in empty space, that light is an electromagnetic wave
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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
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LET US SUMMARIZE THE
PROPERTIES OF
ELECTROMAGNETIC WAVES
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
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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
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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
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ENERGY CARRIED BY
ELECTROMAGNETIC WAVES
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.
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ENERGY CARRIED BY
ELECTROMAGNETIC WAVES
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
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ENERGY CARRIED BY
ELECTROMAGNETIC WAVES
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
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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
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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.
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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
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THE SPECTRUM OF
ELECTROMAGNETIC WAVES
All forms of the various
types of radiation are
produced by the same
phenomenon –
accelerating charges
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POLARIZATION OF LIGHT
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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.
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CLASSIFICATION OF POLARIZATION
Linear Polarization A plane electromagnetic wave is said to be linearly
polarized. The transverse electric field wave is
accompanied by a magnetic field wave
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CLASSIFICATION OF POLARIZATION
Circular PolarizationThe light consists of two perpendicular
electromagnetic plane waves of equal amplitude and
90o difference in phase.
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CLASSIFICATION OF POLARIZATION
Elliptical PolarizationThe light consists of two perpendicular waves of
unequal amplitude which differ in phase by 90o.
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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
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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)
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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