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Electromagnetic Waves & the Electromagnetic Spectrum. Electricity can be static, like what holds a balloon to the wall or makes your hair stand on end. . Magnetism can also be static like a refrigerator magnet. But when they change or move together, they make waves - electromagnetic waves.

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Magnetism can also be static like a refrigerator magnet.

  • But when they change or move together, they make waves - electromagnetic waves.
electromagnetic waves
Electromagnetic waves
  • Formed when an electric field (blue arrows) couples with a magnetic field (red arrows).
  • The magnetic and electric fields of an em wave are perpendicular to each other and to the direction of the wave.
electromagnetic waves1
Electromagnetic Waves
  • Transverse waves without a medium!
  • (They can travel through empty space)
They travel as vibrations in electrical and magnetic fields.
    • Have some magnetic and some electrical properties to them.
When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other.
  • RESULT-An electromagnetic wave.
Electromagnetic waves travel VERY FAST – around 300,000 kilometres per second (the speed of light).

At this speed they can go around the world 8 times in one second.

Waves or Particles?
  • Electromagnetic radiation has properties of waves but also can be thought of as a stream of particles.
    • Example: Light
      • Light as a wave: Light behaves as a transverse wave which we can filter using polarized lenses.
      • Light as particles (photons): When directed at a substance light can knock electrons off of a substance (Photoelectric effect)
Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency









Notice the wavelength is

long (Radio waves) and gets shorter (Gamma Rays)

ionizing radiation vs non ionizing radiation
Ionizing Radiation vsNon-ionizing Radiation
  • Ionizing
    • radiation that is strong enough to damage molecules and cells
    • includes the higher frequency forms of UV radiation, all X-radiation and all gamma radiation
  • Non-ionizing
    • includes the lower frequency forms of UV radiation, and all forms of radiation “below”(visible, IR, microwave, and radio wave radiation).
Background radiation: Low levels of radiation from both natural and man-made sources that is always around us.
  • Natural background radiation examples
    • gamma radiation that penetrates our atmosphere from outer space
    • radiation released from rocks, soil, and water.
  • Man-made sources of radiation
    • fallout from nuclear weapons testing
    • radiation released into the environment from coal-burning and nuclear power plants.
radio waves
  • Have the longest wavelengths and lowestfrequencies of all the electromagnetic waves.
Global Positioning Systems (GPS) measure the time it takes a radio wave to travel from several satellites to the receiver, determining the distance to each satellite.
A radio picks up radio waves through an antenna and converts it to sound waves.
    • Each radio station in an area broadcasts at a different frequency.
      • # on radio dial tells frequency.


    • Uses Short wave radio waves with a magnet to create an image.
  • Have the shortest wavelengths and the highest frequency of the radio waves.
Used in microwave ovens.
  • Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food.

(Radio Detection and Ranging)

  • Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.
infrared rays
  • Infrared= below red
  • Shorter wavelength and higher frequency than microwaves.
A remote control uses light waves just beyond the visible spectrum of light—infrared light waves—to change channels on your TV.
You can feel the longest ones as warmth on your skinWarm objects give off more heat energy than cool objects.
Therefore people give off infrared rays.

Heat lamps give off infrared waves.

Thermogram—a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off.

visible light
  • Shorter wavelength and higher frequency than infrared rays.
  • Electromagnetic waves we can see.
  • Longest wavelength= red light
  • Shortest wavelength= violet (purple) light
ultraviolet rays
  • Shorter wavelength and higher frequency than visible light
  • Carry more energy than visible light
uv waves are invisible to the human e ye
UV Waves are Invisible to the Human Eye
  • Bees, along with some birds, reptiles and other insects, can see near-ultraviolet light reflecting off of plants.
  • Bug zappers attract insects with ultraviolet light to lure them to the trap.
x rays
  • Shorter wavelength and higher frequency than UV-rays
  • Carry a great amount of energy
  • Can penetrate most matter.

Bones and teethabsorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed)


Too much exposure can cause cancer

    • (lead vest at dentist protects organs from unnecessary exposure)
Used by engineers to check for tiny cracks in structures.
    • The rays pass through the cracks and the cracks appear dark on film.
gamma rays
  • Shorter wavelength and higher frequency than X-rays
  • Carry the greatest amount of energy and penetrate the most.
sources of gamma rays
  • Produced by the hottest and most energetic objects in the universe
    • neutron stars and pulsars
    • supernova explosions
    • regions around black holes
  • On Earth - generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay.
gamma rays in medicine
Gamma Rays in Medicine
  • They are able to penetrate most materials and aren't easily blocked.
  • When they pass through matter, they eject electrons from the atoms they collide with.
    • This is called ionization, and it's dangerous to living cells; prolonged gamma radiation can lead to grave illness and even death.
  • Yet we use gamma rays from cobalt-60 for cancer treatment.
  • We also use gamma rays in industry to test castings and welded joints for tiny, almost invisible cracks or defects.
Used in radiation treatment to kill cancer cells.
  • Can be very harmful if not used correctly.
gamma knife surgery
Gamma Knife surgery
  • > 200 beams of gamma radiation are directed at small tumors
    • causing 90 to 95 % of them to cease growing and a majority of them to shrink
    • malignant and benign tumors and Parkinson's disease.
  • PET (Positron Emission Tomography) scan
    • patient is injected with a radioactive substance and placed on a table that slides into a gamma ray detector.
    • Doctors can then track blood flow and other biochemical processes within the body
i nternational s ecurity and food s afety
International Security and Food Safety
  • Container Security Initiative
  • By 2008, 58 ports worldwide were equipped with X-ray and gamma ray screening devices, giving security officers access to 86 percent of all maritime cargo in containers
  • “Irradiation pasteurization" or “cold pasteurization”
    • passing food through a beam of gamma rays
    • kills bacteria that could spoil food or render it poisonous
    • food that is irradiated today does not become radioactive itself, and is considered safe.
in conclusion
In Conclusion…
  • All forms of electromagnetic radiation have important applications and uses
  • Exposure to non-ionizing radiation (lower frequency) forms of EMR is relatively harmless
  • Exposure to ordinary forms and amounts of radiation is not harmful (you have been exposed to all forms of EMR every day of your life)
  • Among those forms to which we should limit our exposure, there are important and helpful uses
  • We can harvest the energy in the electromagnetic radiation from the sun to produce power
Continued SUMMARY
  • All electromagnetic waves travel at the same speed. (300,000,000 meters/second) in a vacuum.
  • They all have different wavelengths and different frequencies.
    • Long wavelength-lowest frequency
    • Short wavelength highest frequency
    • The higher the frequency the higher the energy.