Finish spectrum, visible light, energy of EM waves

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Finish spectrum, visible light, energy of EM
waves
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Type of wave Wavelength Source Uses Danger Interesting
Radio ?gt 30 cm Types of transmitters, stars, sparks, and lightning Communication None.
Microwave 30cm gt?gt 1mm magnetron. Radar, microwave ovens, communication, weather radar Cataracts, being cooked Microwave ovens are shielded (look for the thin wire mesh in the door) People who work on aircraft carrier decks wear special suits which reflect microwaves, to avoid being "cooked" by the powerful radar units in modern military planes.
Infrared 1mm gt?gt 700nm Hot objects, including flames, stars, and warm bodies Weather, TV remotes, heal sports injuries, alarms. Overheating Night vision goggles, weapon targeting systems,
Visible 700nm gt?gt 400 nm Anything hot enough to glow Vision, CD players, laser pointers Damage to retina if you look at something too bright for too long
Ultraviolet 400nm gt?gt 60 nm UV lights, VERY hot objects such as the sun Sun burns, astronomy Sunburn, skin cancer, and damage to retina Be sure to get sunglasses that block UV radiation
X Ray 60nm gt?gt 10-4 nm Stars and nebula, X-ray machines. To see inside people or luggage, astronomy Cancer, damage to cells and DNA X-ray machine works by firing a electron beam at a target.
Gamma Ray ?lt0.1nm Stars and radioactive substances Sterilize medical equipment and food, radiation treatment Cancer, mutations, and kills cells
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Radios How do they work?

• AM radio AM stands for amplitude modulation.
• Set frequency but radio station varies the
  amplitude
• Problems
• Lots of natural and man-made noise.
• Weak signals are quieter than strong ones.

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Radios How do they work?

• FM radio FM stands for frequency modulation.
• Set amplitude but radio station varies the
  frequency

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Microwave ovens

• Water. There are trillions of water molecules in
  a single drop. The temperature of the water
  depends on the motion of the molecules. They move
  with respect to each other and vibrate.
• The hotter the water, the more activity.

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Microwaves continued

• Water molecules absorb microwaves at a certain
  frequency. This extra energy causes an increased
  amount of vibrations in the molecules.
• As the water molecules vibrate, they bump into
  other molecules, transferring energy or heat.

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Visible Light

• A few things you need to know
• For Violet light, ? 400 nm
• For red light, ? 700 nm
• Example Compare the frequency of red light
  compared to violet light.

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Visible Light

• cf? Plug in the numbers
• Red ? 700 nm 70010-9 m
• Violet ? 400 nm 40010-9 m
• C3.00108 m/s
• Frequency of Red light4.31014 Hz
• Frequency of Violet light7.51014 Hz
• Notice the trend, Violet has a higher frequency
  than Red

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Light Particle

• PhotonA discrete unit of light energy
• A photon is localized energy

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Energy of a Photon

• Ehf
• Energy constant frequency
• hPlancks constant6.62610-34 J Sec

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Example

• What is the energy of a photon of green light?
  Wavelength 550nm
• The equation is Ehf. First, find the frequency
  of green light.
• ?550 nm 55010-9 m
• Cf ?, f5.451014Hz
• Ehf, h6.6210-34Jsec
• E3.6010-19 J

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Example 2

• If the energy of a photon is 2.510-18 J, what is
  the frequency of that photon? What is the
  wavelength?
• Answer Frequency 3.771015 Hz
• Wavelength 7.94410-8 m