ElectroMagnetic Radiation Spectrum

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ElectroMagnetic Radiation Spectrum

• The basics about light and waves

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Breakdown

• 1.) Terms to Know
• 2.) What is the E.M.R. Spectrum?
• 3.) How does light travel?
• 4.) Characteristics of a wave and light

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Terms to know

• 1.) Radiation - process of emitting radiant
  energy (light) in the forms of
• waves and particles
• 2.) Electron - subatomic particle of atoms with a
  negative charge and the
• least mass usually found orbiting the nucleus
• 3.) Magnetic fields - lines of force that connect
  the positive and negative
• areas of a magnetic body
• 4.) Waves - movement of energy through a medium
  or empty space in the
• pattern of a sine wave
• 5.) Spectrum - a continuous sequence or range in
  this case, the
• wavelengths of light

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The E.M. Spectrum

• - The Electromagnetic spectrum is the full range
  of wavelengths that light can travel in

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The E.M. Spectrum

• - light, or radiation, travels at a constant
  speed in a vacuum
• c 300,000 km / s
• - there are many different types of light, but
  they all share the same speed
• Visible, Ultraviolet (UV), Infrared (IR),
  X-rays, Microwaves,
• Gamma Rays, and Radio Waves

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How does light travel?

• - Light, depending on how you study it, can have
  the properties of waves or particles
• The EM spectrum breaks down the types of light
  based on wavelength so we will focus on waves
• Light is special in that its waves do not
  require a medium to travel through
• ex there is no sound in the vacuum of space
  because there is no matter for it to travel
  through

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Waves

• - 2 types of waves
• Transverse and Longitudinal
• - Even though matter may be moving (up, down, and
  all
• around), it does not travel with the waves,
  only energy
• is being passed along. This is true with
  all waves.
• - Wavelength distance between two crests or two
  troughs
• (in the case of longitudinal waves, the distance
  between
• two areas of compression)
• measured in SI units (meters)

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Longitudinal Waves

• Waves that travel parallel to the direction of
  motion
• Made up of compressions and rarefactions in the
  medium that they are traveling in
• Examples sound waves and s waves for earthquakes

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Transverse Waves

• Waves that travel perpendicular to the direction
  of
• displacement
• Examples Light, p waves
• for earthquakes, Ocean waves

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Misconception

• - As you should have seen, Radio Waves are a type
  of light and therefore are not sound.
• Sound waves Radio waves !
• - You may ask But I hear sound from my
• radio, how is this possible?
• - Because of the nature of light, sound
  information can be encoded in Radio waves and
  later extrapolated back out as sound
• .... how this is done is a topic for another time

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Characteristics of a Wave

• There are 4 basic components to any transverse
  wave such as light
• Amplitude
• Frequency
• Phase
• Polarization

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1.) Amplitude

• - Amplitude is the total displacement of a wave.
  
• In simple terms, it is the distance from the
  middle of a wave to its peak

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2.) Frequency

• - Number of crests (or wavelengths) passing by
  per second
• - Measured in Hertz (Hz), meaning cycles per
  second
• - Equals the inverse of the time it takes for one
  wavelength to pass by
• f 1 / t

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3.) Phase

• - Phase is the initial angle of a sinusoidal
  function at its origin
• - If two waves are the same or similar in phase,
  they will add together
• - If they offset enough, they will subtract

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4.) Polarization

• - Polarization is the orientation of oscillations
  in the plane perpendicular to a transverse wave's
  direction of travel
• Different polarizations are cause by the electric
  and magnetic fields being out of phase from one
  another
• - Possible Polarizations
• horizontal
• vertical
• circular
• elliptical

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Other properties of light

• Because of lights characteristics and physical
  nature, light has some other interesting
  properties
• Diffraction
• Refraction
• Scattering

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Diffraction of Light

• Diffraction of light is the interference of its
  waves when it encounters an opening or an
  obstacle.
• - Seen when the obstacle or opening
• matches up closely with the waves
• wavelength
• - Longer wavelengths get diffracted more
• than shorter wavelengths

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Diffraction of Light (cont.)

• The effects of diffraction are most easily
  examined via the single-slit and double-slit
  experiments
• Based on the size of slits used in comparison to
  the wavelengths of light, different patterns of
  interference result

1 x
5 x
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Refraction of Light

• Refraction is the bending, or change in direction
  of light as it passes from one medium to another
• - The secondary medium has a different
• refractive index from the first

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Refraction of Light (cont.)

• If you have ever looked at an object underwater
  from above, you have witnessed refraction.
  Because light gets bent as it changes mediums
  from the air to the water, the image you see
  becomes distorted.

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Refraction of Light (cont. x 2)

• - A prism works based on this concept. As light
  enters a prism, the light gets bent as it passes
  from one medium to the other. -Prisms take it a
  step further and bent each wavelength of light
  differently
• This spreads the light out into a rainbow of
  color as you may have seen.
• The shorter wavelengths bend more than the longer.

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Scattering of Light

• Light scattering is the deflection of an incident
  beam of light off any irregular portion of the
  medium in which it is passing through.
• Light scatters off of any surface generally
  speaking, and the type of light being scattered,
  or reflected, is the color in which you see.

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Why is the sky blue?

• The atmosphere is a collection of gases that is,
  for the most part, evenly distributed. As light
  passes through it, light randomly strikes small
  particles and molecules suspended in the air
  column. Because of this, light gets scattered in
  all directions.
• Shorter wavelengths are more easily scattered, so
  blue light gets scattered more.

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What about dusk and dawn...

• You may notice when the sun rises and sets, the
  sky is no longer blue but instead more of a
  yellow/red hue. During these times, sunlight
  enters the atmosphere at a more extreme angle and
  must pass through more atmosphere to reach your
  eyes. By this time, all or most of the shorter
  wavelengths have been scattered leaving only the
  longer wavelengths.

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If shorter wavelengths scatter more easily...

• Then why isnt the sky violet?
• - There just isnt enough violet light
• being emitted from the Sun. The sun
• because of its temperature gives off
• much more blue light therefore it is
• more prevalent.