Chapter 9.1 Notes

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Transcript Chapter 9.1 Notes

Chapter 9.1
Notes
Electromagnetic Waves
Part 1
• A changing electric field can
produce a changing Magnetic
Field.
• A changing magnetic field can
produce a changing Electric
Field
• The combination of these two
fields is what produces an
Electromagnetic Wave.
• Changing current can produce
changing electric and magnetic fields
that move away from an antenna at
the speed of light and are called
Electromagnetic Wave.
• The energy is contained in the
electric and magnetic field or in the
electromagnetic wave and this
energy is called Electromagnetic
Radiation.
• Electromagnetic waves travel
at 300,000,000 m/s through a
vacuum.
• 300,000,000 m/s is the same
speed as the speed of light.
• We use the letter c to
represent the speed of an
electromagnetic wave.
Speed of Light Demo
• The speed in the air is approximately
the same as the speed in a vacuum.
• All electromagnetic waves travel at
the same speed, but they can have
different frequency and
wavelength.
• Equation for wavelength and
frequency = speed = wavelength x
frequency
• c = λƒ
• If our frequency is 1200 H, what is
the wavelength?
• c = λƒ
• c = 300,000,000 m/s
• 300,000,000 m/s = λ x 1200 H
• 300,000,000 / 1200 = λ
• Hertz = 1/s so the seconds cancels
and leaves meters only.
• λ = 250,000 m
• The wavelength of a wave is
the distance between peak of
the electric field or magnetic
field in the wave.
• The frequency is the rate at
which peaks pass a stationary
point.
• Wavelengths of electromagnetic
waves range from millions of
meters to as short as
.0000000000000016 meters.
• The range of wavelengths and
frequencies of electromagnetic
waves is called the
electromagnetic spectrum.
• The electromagnetic spectrum
is divided into bands, based
on sizes of the wavelengths of
electromagnetic waves.
• Radio Waves are the longest
electromagnetic waves, some
as long as several thousand
kilometers.
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List the electromagnetic bands in
order:
Longest
1 Radio Waves
2 Microwaves
3 Light Waves
4 X Rays
5 Gamma Rays
Shortest
6 Cosmic Rays
•Light is broken into
3 categories:
1. Ultraviolet
2. Visible
3. Infrared
• Radio waves are used to transmit radio
and television signals.
• Radio wavelengths can be less than 1
centimeter long or even hundreds of
kilometers long.
• At the radio or TV station, they have
transducers that are used to convert
sound into electric signals which creates
an electromagnetic wave.
• These radio waves are than transmitted
in all directions from an antenna.
• The waves travel to a receiving antenna
and move at the speed of light
(300,000,000 m/s).
• At the receiving antenna, there is
another transducer that changes the
electromagnetic wave back into sound.
• Each type of radio waves has a
different wavelengths. For example,
waves from a radio station are longer
than waves emitted by your cell phone.
• Microwave radiation has shorter
wavelengths and higher
frequencies than radio waves.
• Microwave wavelengths range
from approximately one
millimeter (the thickness of a
pencil lead) to thirty centimeters
(about one foot).
• Microwaves are used in
telecommunication. They carry
information from point to point on
the Earth, or from Earth to satellites.
• Microwaves are also used in radar
systems to detect and track moving
objects.
• The direction of the reflected wave
can be measured to locate the object.
• The reflected wave frequency is
changed if the object is moving
and this change can be measured
and used to determine the object’s
speed.
• In a microwave, the
electromagnetic waves that are
generated are tuned to
frequencies that can be absorbed
by water molecules.
Microwave Demos
• Lightbulb
• CD
• Soap