Let there be light

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Let there be light

• Most of what we know about the Universe comes
  from information that has been carried to us by
  light.
• We will begin by examining the properties of
  light and then we will discuss the instruments
  that are used to detect it (telescopes).t.

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Light Basics

• Light is radiant energy
• Radiant energy is energy that can travel through
  space from one point to another without the need
  of a direct physical link
• In empty space light travels at a constant speed,
  299,792.458 kilometers per second (this is a
  constant and is denoted by c).
• Fast enough to circle the Earth over 7 times in
  one second!
• When light travels through matter, glass, water,
  gasses, etc. it slows down.
• Light can be thought of one of two ways
• 1. As an electromagnetic wave a mix of electric
  and magnetic energy

• 2. As photons photons are packets of energy
• Both models have one thing in common they
  classify light as being energy

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Light As A Wave

• Parts of an electromagnetic wave
• Crest the high point of a wave
• Trough the low point of a wave
• Wavelength (?) the distance of two
  wavecrests or two wavetroughs

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Looking At Waves Through Sound

• We cant see light waves, but we can look at
  sound waves to help us understand wave structure
  and wave energy.

• Which one of these wave models has the bigger
  wavelength?
• Which one of these models has the greater
  frequency?

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The Difference Between Light and Sound Waves

• We use sound waves to hear. Even though sound has
  the same wave structure as light they are
  fundamentally different.
• Sound energy relies on the vibration of sound
  waves through matter.

• Light is a form of radiation
• It is not dependant on matter to get form one
  place to another.

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Light is Radiation!!!! Oh No!!!!

• Yes, light is radiation. It is one of many types
  of radiation. All this means is that it can
  travel through space without the need for a
  direct transfer of energy.
• Sound was the opposite. It moves because of a
  direct transfer of energy from one particle to
  another

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Types of Radiation
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So now the BIG question, what separates one type
of radiation from another?

• They are all related
• All have wave properties
• Crest, trough, and wavelength
• What separates one from another however is
  frequency
• Wave Frequency Energy
• High frequency high energy
• Low frequency low energy

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• High Frequency

• Low Frequency

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What does this have to do with anything?

• Well, since we already know that there are
  different types of radiation, we should now
  investigate why one different from another
• Each of the energies we discussed is radiant
  energy (radioactive energy).
• What separates one from another is the frequency
  at which they radiate.
• Higher frequency ? Energy ? Wavelength
• Lower frequency ? Energy ? Wavelength

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So..
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Looking at the whole spectrum of electromagnetic
energy
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How do we know this model is correct?

• We can use what we already know and some simple
  concepts to help us out.
• We know that every form of radiation behaves as a
  wave
• We also know that each type of radiation moves at
  a constant speed through empty space (c)
• Furthermore, we know that some waves have a
  higher frequency than others
• Lastly we know that different radiations
  different wavelengths

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Looking at it another way
Wavelength (?) x Frequency (f) The Speed of
Light (c) Or ? x f c

• When we look at this we can notice a couple of
  things
• The speed of light (c) is a constant (3.0 x 108
  meters/sec)
• High frequency short wavelength
• Low frequency large wavelength
• Wavelength and frequency are inversely
  proportional

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So how do we use this?

• The numbers on a radio dial for FM
  stations are their frequencies in megahertz
  (MHz), or millions of hertz. If you listen to
  93.1 WXRT, it broadcasts radio waves with a
  frequency of 93.1 million cycles per second
  (1/sec). What is the wavelength of these radio
  waves?
• We know two things
• The speed of light 3 x 108 m/sec
• The frequency 9.31 x 107 1/sec
• Now its just plug and chug

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The Solution
? x f c Solve for ? ? c/f
? 3.2 meters
Now you try it for 97.1 The Drive, but before you
do, will the wave length be bigger or smaller
than XRTs?
Did you get 3.09 meters?
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Wait, what about energy? How is energy related to
? c/f ?

• To help us with this lets take a small trip to
  this place and learn about a guy named Max
  Planck.
• Now we have Plancks constant (h)
• Planck said that Energy (E) h (constant) x
  frequency (f)
• If we take ? x f c and solve for frequency(f),
  than we get
• f c/ ?
• If we plug this into E h x f we then have