The Basics of Light

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The Basics of Light
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• One thing that all
• the forms of electromagnetic radiation have
  in common is that they can travel through empty
  space.

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Electromagnetic Radiation

• Electromagnetic radiation or light is a form of
  energy.

• Has both electric (E) and magnetic (H) components.

• Characterized by
• Wavelength (l)
• Amplitude (A)

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• Visible light waves are the only
  electromagnetic waves we can see. We see these
  waves as the colors of the rainbow. Each color
  has a different wavelength. Red has the longest
  wavelength and violet has the shortest
  wavelength. When all the waves are seen together,
  they make white light.

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The Particle/Wave Duality

• Light is a particle
• but it has no mass
• blue light can knock electrons off metal plate
• red light cant has less energy
• Light is a wave
• light goes out in all directions
• light bends around corners (like waves around a
  pier)
• light reflects (mirrors)
• light refracts (bends)

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INTERFERENCE of the light
Interference is the interaction between waves
traveling in the same medium.
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Electromagnetic Spectrum
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Electromagnetic Radiation (cont.)

• We classify electromagnetic radiation by
  wavelength.

• Visible radiation takes up only a small part of
  the electromagnetic spectrum.

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The Electromagnetic Spectrum
Radio
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Radio Waves

• Created by oscillations (vibrations) of electrons
  in a conductor.
• Very long wavelength (few km to few cm) low
  frequency so low energy waves.
• Used to transmit radio and TV signals.
• Travel in straight lines, but can be bounced off
  the upper atmosphere, so can travel around the
  world.

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Radio
Radio waves are very long compared to waves from
the rest of the spectrum Radio telescopes use a
large metal dish to help detect radio waves
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The Electromagnetic Spectrum
Radio
Micro- Waves
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MICROWAVES

• Wavelength from cm to .0001 m
• Used for cooking food
• Microwaves make water molecules vibrate, which
  causes food to get very hot very quickly.
• Penetrate only a few cm, the heat is then carried
  inside by conduction

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MICROWAVES

• Microwaves are also used for communication.
• Mobile telephones use microwaves.
• They are also used to communicate with satellites
  as they can pass through the upper atmosphere
• They also do not spread out much, so they are
  easy to use with a dish.

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The Electromagnetic Spectrum
Infra Red
Radio
Micro- Waves
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INFRA-RED

• Everything gives out Infra-red
• This allows cameras to use IR instead of visible
  light for night-vision.
• They are also used for thermo-imaging cameras, to
  find people buried in earthquakes. They will be
  being used in New York.
• They are also used for remote controls

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Infrared Radiation
Wavelength 1 um 1000 um

• We emit IR light. In fact all the objects around
  us emit IR radiation. Hotter objects emit more
  IR radiation, which we are warmed by, and which
  we sense with our skin.

IR photo of a man
IR photo of the dust in the Solar System
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The Electromagnetic Spectrum
Infra Red
Radio
Micro- Waves
Visible
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Visible Light
White light is made up of light from all
different colors
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Intensity of Light

• Intensity is lowered when the light is spread
  out.

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The Electromagnetic Spectrum
Infra Red
Ultra Violet
Radio
Micro- Waves
Visible
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ULTRA VIOLET

• Shorter wavelength 0.000001m to 0.000000001m,
  frequency higher.
• Carry more energy, and can penetrate top layers
  of skin, damaging the lower layers
• This can cause sun burn, and possibly skin cancer
  of a long period of time.
• The eyes are very sensitive to UV, so sunglasses
  should always be worn in bright sunshine.
• Most UV radiation from the sun is filtered by the
  ozone layer.

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Ultraviolet Light
Some birds bees can see UV as well as visible
light.
Ultraviolet light has just the right energy to
break molecular bonds apart. For this reason it
is detrimental to life. The Earth has a natural
shield to Solar UV light in the form of an ozone
layer (80 km above the surface).
10 of sunlight is in the UV
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The Electromagnetic Spectrum
Infra Red
Ultra Violet
Radio
Micro- Waves
Visible
X-Rays
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X-Rays

• Their ability to pass through soft tissue, but
  not bone, makes them very useful in medicine.
• They are completely stopped by metals, making
  them useful for security scanning at airports.

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X-Rays

• Because they carry a lot of energy they can
  easily damage or kill cells.
• This can lead to cancer if over-exposure occurs.
• Very small amounts are used in hospitals and are
  relatively safe, however the operator will stand
  behind a lead screen to stop unnecessary exposure
• X-rays are also used to treat cancer by killing
  cancerous cells.

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The Electromagnetic Spectrum
Gamma Rays
Infra Red
Ultra Violet
Radio
Micro- Waves
Visible
X-Rays
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X-Rays and Gamma Rays

• X-rays and gamma rays absorbed in the Earths
  atmosphere
• observatories must be sent into space
• produced by matter heated to millions of
  degrees
• caused by cosmic explosions, high speed
  collisions

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X-rays
X-rays were discovered 1895 by Wilhelm Conrad
Roentgen (a German scientist) by accident. A
week later he took this x-ray of his wife.
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Gamma Rays for Medicine

• Gamma rays are used in medicine to kill and treat
  certain types of tumors and cancers.
• .

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RISKS and BENEFITS

• X-Rays and Gamma rays are both used in medicine.
• Their benefits are they destroy cancer, and avoid
  surgery, as well as use for diagnostic purposes.
• They can also cause cancer, and may cause
  sickness if exposures are too large.

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THE COMPLETE ELECTROMAGNETIC SPECTRUM
Long
Short
WAVELENGTH
Gamma Rays
Infra Red
Ultra Violet
Radio
Micro- Waves
Visible
X-Rays
FREQUENCY
Low
High
ENERGY
Low
High