Transcript electromagnetic wave.

Electromagnetic Waves &
the Electromagnetic Spectrum
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Electromagnetic Waves
• Transverse waves without a medium!
• (They can travel through empty space)
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• They travel as vibrations in
electrical and magnetic fields.
– Have some magnetic and some
electrical properties to them.
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• When an electric field changes, so does
the magnetic field. The changing
magnetic field causes the electric field
to change. When one field vibrates—so
does the other.
• RESULT-An electromagnetic wave.
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• Electromagnetic waves travel
• VERY FAST
• around 300,000,000 m/s
• the speed of light
At this speed they
can go around the
world 8 times in one
second.
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•
•
Waves or Particles?
Electromagnetic radiation has properties
of waves but also can be thought of as a
stream of particles.
•
Light as a wave: Light behaves as a transverse
wave which we can filter using polarized lenses.
•
Light as particles (photons): When directed at a
substance light can knock electrons off of a
substance (Photoelectric effect)
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• Electromagnetic Spectrum—name for the
range of electromagnetic waves when
placed in order of increasing frequency
RADIO
WAVES
INFRARED
RAYS
MICROWAVES
ULTRAVIOLET
RAYS
VISIBLE LIGHT
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GAMMA
RAYS
X-RAYS
Notice the wavelength is
long (Radio waves) and gets shorter (Gamma Rays)
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RADIO WAVES
• Have the
longest
wavelengths and
lowest
frequencies of
all the
electromagnetic
waves.
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• Global Positioning Systems (GPS)
measure the time it takes a radio wave to
travel from several satellites to the
receiver, determining the distance to
each satellite.
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• A radio picks up radio waves through an
antenna and converts it to sound waves.
– Each radio station in an area broadcasts at a
different frequency.
• # on radio dial tells frequency.
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MRI
(MAGNETIC RESONACE IMAGING)
Uses Short wave radio waves with a
magnet to create an image.
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MICROWAVES
• Have the
shortest
wavelengths and
the highest
frequency of
the radio
waves.
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Used in microwave
ovens.
• Waves transfer
energy to the
water in the food
causing them to
vibrate which in
turn transfers
energy in the
form of heat to
the food.
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RADAR (Radio
Detection and
Ranging)
• Used to find the
speed of an object
by sending out radio
waves and measuring
the time it takes
them to return.
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INFRARED RAYS
• Infrared=
below red
• Shorter
wavelength and
higher
frequency than
microwaves.
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•
You can feel
the longest ones
as warmth on
your skin
Warm objects
give off more
heat energy than
cool objects.
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Thermogram—a picture that shows regions of different
temperatures in the body. Temperatures are calculated by
the amount of infrared radiation given off.
•Therefore people give
off infrared rays.
•Heat lamps give off
infrared waves.
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VISIBLE LIGHT
• Shorter wavelength and
higher frequency than
infrared rays.
• Electromagnetic waves
we can see.
• Longest wavelength=
red light
• Shortest wavelength=
violet (purple) light
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When light enters
a new medium it
bends (refracts).
Each wavelength
bends a different
amount allowing
white light to
separate into it’s
various colors
ROYGBIV.
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ULTRAVIOLET RAYS
• Shorter
wavelength and
higher
frequency than
visible light
• Carry more
energy than
visible light
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• Used to kill
bacteria.
(Sterilization
of equipment)
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• Too much can cause skin cancer.
• Use sun block to protect against
(UV rays)
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• Causes your
skin to
produce
vitamin D
(good for
teeth and
bones)
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X- RAYS
• Shorter
wavelength and
higher
frequency than
UV-rays
• Carry a great
amount of
energy
• Can penetrate
most matter.
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Bones and teeth absorb x-rays. (The light part
of an x-ray image indicates a place where the xray was absorbed)
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Too much exposure
can cause cancer
(lead vest at
dentist protects
organs from
unnecessary
exposure)
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• Used by
engineers to
check for tiny
cracks in
structures.
– The rays pass
through the
cracks and the
cracks appear
dark on film.
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GAMMA RAYS
• Shorter wavelength
and higher frequency
than X-rays
• Carry the greatest
amount of energy
and penetrate the
most.
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• Used in radiation treatment to
kill cancer cells.
• Can be very harmful if not used
correctly.
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• The
Incredible
Hulk was the
victim of
gamma
radiation.
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Exploding
nuclear
weapons emit
gamma rays.
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Frequency Ranges
• Wavelengths
• 104
101 1
10-2 10-5 10-6 10-8
10-10
10-12
• Frequencies (cycles per sec)
3 x 106
3 x 1010
3 x 1014
3 x 1016 3 x1018
3 x10 22
• Brief SUMMARY
• A. All electromagnetic waves travel at
the same speed. (300,000,000
meters/second) in a vacuum.
• B. They all have different wavelengths
and different frequencies.
– Long wavelength-lowest frequency
– Short wavelength highest frequency
– The higher the frequency the higher the
energy.
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C (speed of EMS waves) = λf
• The frequency (f) of a wave is the
number of waves to cross a point
in 1 second (units are Hertz –
cycles/sec or sec-1)
• λ is the wavelength- the distance
from crest to crest on a wave
• The product of wavelength and
frequency always equals the
speed of light.
C = λf
• Why does this make sense?
• NOTE:
c is a constant value= 3.00 x 108 m/s
PROBLEMS
• Calculate the wavelength of yellow light
emitted from a sodium lamp if the
frequency is
5.10 x 1014 Hz (5.10 x 1014 s-1)
List the known info List the unknown
c = 3.00 x 1010 cm/s
wavelength (λ) = ? cm
Frequency (v) = 5.10 x 1014 s-1
C = λf
λ=c
f
λ = 3.00 x 1010 cm/s = 5.88 x 10-5 cm
5.10 x 1014 s-1
YOUR TURN
1- What is the wavelength of radiation
with a frequency of 1.50 x 1013 s-1?
2- What
frequency is radiation with a
wavelength of 5.00 x 10-6 cm? In what
region of the electromagnetic
spectrum is this radiation?
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