Electromagnetic Waves Chapter 3

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Electromagnetic WavesChapter 3

• Electromagnetic Spectrum Lesson 3-1

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Types of Waves

• Longitudinal Waves
• Transverse Waves

http//www.thetech.org/exhibits/online/quakes/wave
s/ps_waves.html
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Longitudinal Waves

• Longitudinal Waves one in which the disturbance
  is parallel to the line of travel of the wave.
  Cannot travel through empty space. The
  wavelength depends on the frequency.

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Longitudinal Wave

• When a longitudinal wave moves through a
  material, the particles of the material move
  backwards and forwards along the direction in
  which the wave is travelling. Below is a picture
  of a longitudinal wave travelling along a spring.

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Longitudinal Wave
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Example of Longitudinal Wave

• Sound Waves
• Sound is always produced by something vibrating.
  The vibrations will make matter - either solid,
  liquid or gas - near it vibrate. In this way,
  energy is taken away from the source of the
  vibrations.
• Sound must cause another object to vibrate to be
  detected.

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• Sound cannot travel in a vacuum because there is
  nothing (no matter) for the vibrations to pass
  through.
• Sound does not travel in outer space.
• When you see movies or TV shows about battles in
  outer space, you should only be able to see an
  explosion but not hear it. The sounds are added
  for dramatic effect.

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• Sound waves exist as variations of pressure in a
  medium such as air. They are created by the
  vibration of an object, which causes the air
  surrounding it to vibrate. The vibrating air then
  causes the human eardrum to vibrate, which the
  brain interprets as sound.

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Sound Facts

• Sound must cause another object to vibrate to be
  detected.
• Sound travels fastest through things that have
  tightly packed atoms solids.   
• The speed of sound is slower in liquids than
  solids, and slowest in gases.
• The speed of sound in air is around 340 m/s, in
  water about 1500 m/s and in solids around
  5000 m/s.     
• Lightning causes thunder. The delay between them
  happens because the speed of light is nearly
  1,000,000 that of sound in air.

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Example of Longitudinal Wave

• Ultrasound
• Ultrasound is sound that is above the range of
  human hearing. It even travels at exactly the
  same speed as sound in any medium. Taking a
  ultrasound of the unborn fetus is a lot safer
  then taking an x-ray.

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• Ultrasounds are used in many different ways from
  looking at valves of the heart, cleaning teeth
  and airplane wings to taking sonar to determine
  the depth of water.

Valves Of Heart Ultrasound
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Example of Longitudinal Wave

• P- Wave (Primary Waves)
• In an earthquake P-waves are longitudinal waves
  that push and pull the earth. They are the
  fastest body wave, averaging speeds of about 6
  km/s, so arrive first.

http//samjshah.com/2008/07/30/earthquakes-richter
-scale-and-logarithms/
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Transverse Waves

• Transverse Waves one in which the disturbance is
  perpendicular to the direction of travel of the
  wave.

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Transverse Waves

• Most waves are transverse waves.
• Such as water waves, S-waves, electromagnetic
  waves

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Example of Transverse Waves

• S-waves (Secondary Waves)
• In an earthquake S-waves are transverse waves
  which make the earth shake from side to side.
  Slower than P-waves, they average about 4 km/s so
  arrive second

http//samjshah.com/2008/07/30/earthquakes-richter
-scale-and-logarithms/
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Transverse Wave

• The highest point on the wave is called the
  crest.
• The lowest point on the wave is called the
  trough.

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Transverse Wave

• Wavelength the distance between one wave crest
  to the next.
• Amplitude the deepest part of a trough or the
  highest part of a peak is called the amplitude

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Transverse Wave

• Frequency the number of waves per second,
  measured in hertz

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Transverse Wave

• Wavelength and frequency are inversely
  proportional. (when one gets larger the other
  gets smaller.) As the frequency of a wavelength
  increases the wavelength get shorter.

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Electromagnetic Waves

• Electromagnetic waves are transverse waves that
  have some electrical and magnetic properties.
  They do not need a medium, matter, to travel
  through.
• Electromagnetic waves transfer energy by means of
  changing electric and magnetic fields.

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• Electromagnetic wave is a combination of electric
  fields and magnetic fields that are turning at
  right angles to each other.

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• It begins with a vibrating electric charge that
• produces an electric field which produces a
• magnetic field which produces an electric field
• which produces a magnetic field that changes
• direction with each vibration of the charge.

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• Electromagnetic waves are formed when an electric
  field (shown as blue arrows) couples with a
  magnetic field (shown as red arrows). The
  magnetic and electric fields of an
  electromagnetic wave are perpendicular to each
  other and to the direction of the wave. James
  Clerk Maxwell and Heinrich Hertz are two
  scientists who studied how electromagnetic waves
  are formed and how fast they travel.

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Electromagnetic Waves

• Electromagnetic waves come in many wavelengths
  and frequencies. Each one is useful in different
  ways.

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Electromagnetic Waves

• Every time the source of an electromagnetic wave
  vibrates, it creates one wave that moves away
  from the source at the speed of light, 300
  million meters per second.

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Frequency Speed/Wavelength
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Electromagnetic Spectrum

• Electromagnetic Spectrum the entire range of
  electromagnetic waves
• Parts of the spectrum have names (from lowest
  frequency to highest frequency)
• Radio waves
• Microwaves
• Infrared Radiation
• Ultraviolet Radiation- Visible Light is at the
  beginning of ultraviolet radiation
• X Rays
• Gamma Rays
• Radiation is the transfer of energy by
  electromagnetic waves

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Electromagnetic Spectrum
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Nature of Light

• Visible Light only small portion of the
  electromagnetic spectrum
• Light is a wave and consists of small particles
  called quanta

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Who discovered the colors of white light?

• Clue
• Discovered over 300 years ago.
• Passed a beam of white light through a prism.
• First took apart white light and then put it back
  together.
• Initials I. N.

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Prism

• Sir Isaac Newton

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Color

• The only color signals the brain receives are
  red, green and blue stimuli

http//home.att.net/RTRUSCIO/SPECTRUM.htm
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Color

• Black is the color of objects that do not reflect
  light in any part of the visible spectrum they
  absorb all frequencies of light.
• White light is all colors, can be separated into
  a rainbow of colors

http//library.thinkquest.org/27066/color/nlchange
s.html
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Reflection

• Light travels in straight lines and can be
  reflected off surfaces
• When the ray of light reflects off a flat
  surface, the angle of incidence is equal to the
  angle of reflection.

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Diffraction

• Diffraction the bending of light around a
  barrier.
• Waves bend in a semi-circular pattern as they
  pass the barrier.

http//www.olympusmicro.com/primer/lightandcolor/d
iffraction.html
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Refraction of Light

• Refraction of Light - occurs as light passes from
  one medium to another only when there is a
  difference in the index of refraction

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Bibliography

• Abramowitz, Mortimer, and Michael W. Davidson.
  "Diffraction of Light." Olympus Microscopy
  Research Center. 2000-2008. Olympus Microscopy
  Research Center. 24 Oct. 2008 lthttp//www.olympusm
  icro.com/primer/lightandcolor/diffraction.htmlgt.
• Glencoe/McGraw-Hill Team. Teacher's for Use with
  Science Interactions Course 3. 3rd ed. New York
  Glencoe/McGraw-Hill, 1998. 80.
• Harmsworth, A. P. "Waves Sound, Ultrasound,
  P-Waves, S-Waves." GCSE Physics. 2005-2008. GCSE
  Physics. 24 Oct. 2008 lthttp//www.gcse.com/waves/s
  ound.htmgt.
• Henderson, Tom. "The Nature of a wave." Glenbrook
  South Physics Teachers. 1996-2008. Glenbrook
  South. 24 Oct. 2008 lthttp//www.glenbrook.k12.il.u
  s/gbssci/phys/class/waves/u10l1c.htmlvocabgt.
• Kurtus, Ron. "Sound Waves." School for Champions.
  26 June 2005. School for Champions. 24 Oct. 2008
  lthttp//www.school-for-champions.com/science/sound
  .htmgt.
• Sample, Sharron. "What are Electromagnetic
  Waves?" National Aeronautics and Space
  Administration. 27 Mar. 2007. NASA Official. 24
  Oct. 2008 lthttp//science.hq.nasa.gov/kids/imagers
  /ems/waves2.htmlgt.