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Electromagnetic Waves

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Electromagnetic Waves & The Electromagnetic Spectrum S8P4 a S8P4 d Waves Most electromagnetic waves are invisible Detect the present of waves by what we can see, feel ... – PowerPoint PPT presentation

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Title: Electromagnetic Waves


1
Electromagnetic Waves The Electromagnetic
Spectrum
  • S8P4 a
  • S8P4 d

2
Waves
  • Most electromagnetic waves are invisible
  • Detect the present of waves by what we can see,
    feel, or hear

3
Electromagnetic Waves
  • Electromagnetic waves are a disturbance that
    transfers energy through a field
  • You have a EM wave when the disturbance occurs in
    a electric or magnetic field rather than in a
    medium

4
Sources
  • The Sun is main source of EM waves and provides
    most of the energy for Earth!
  • Stars also can give off EM waves but their wave
    dont always make it to earth because of the
    distance between the earth and stars
  • Humans use technology to give off EM waves

5
How they travel
  • Energy that moves in the form of EM waves is
    called radiation
  • Mechanical waves must have a medium whereas EM
    waves can travel without a medium-like in a
    vacuum
  • EM waves do not lose energy as they move so they
    can travel forever!

6
Vacuum
  • Sun waves travel 150 million km to reach earth
    (93 million miles)
  • Rays from other galaxies can travel billions of
    years before reaching earth
  • Waves in a vacuum spread out and travel until
    something interferes
  • The further they travel, the more they will
    spread and the less waves in a area (which means
    less energy being transferred to the area in
    which the wave will encounter)

7
Speed
  • Travel at a constant speed and very fast (300,000
    km per second)
  • Sun rays take 8 minutes to reach Earth
  • This constant speed is called the speed of light

8
EM Waves and mediums
  • When EM waves encounters a medium, it will react
    with it just like a mechanical wavethey transfer
    energy to the medium
  • They will also reflect, refract, or diffract
    which causes the energy to change direction

9
Answer the following questions
  1. How are EM waves different from mechanical waves?
  2. What are two sources of EM waves in Earths
    environment?
  3. How can EM waves transfer energy differently in a
    material medium as compared to a vacuum?
  4. What might be one cause of uneven heating in a
    microwave oven?

10
The Electromagnetic Spectrum
  • S8P4a

11
Electromagnetic Waves
  • Electromagnetic waves come in many wavelengths
    and frequencies. Each one is useful in different
    ways.

12
Electromagnetic Spectrum
  • The electromagnetic spectrum is the range of all
    EM frequencies
  • The EM spectrum is a smooth, gradual progression
    from the lowest frequencies to the highest (and
    wavelengths)

13
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14
Radio Waves
  • Waves that have the longest wavelength, the
    lowest frequency, and lowest energy
  • Travel easily through the atmosphere and
    materials
  • Radio waves are broadcasted by a transmitter
    where a receiver picks up the signals and
    converts it to sound waves
  • Radio stations use different frequencies so they
    dont get crossed

15
Radio Waves
  • Two ways to modulate radio wave is by changing
    the amplitude and varying the frequency
  • Amplitude is used for AM
  • Frequency is used for FM
  • Televisions also use radio wavesthey use AM
    signals for the picture and FM for the sound

16
Microwaves
  • Have shorter wavelengths, higher frequencies, and
    higher energy than other radio waves
  • Important uses of microwaves are radars and cell
    phones
  • Radars (WWII) transmits microwaves, receives
    reflections, and converts it into visual images
  • Radar led to the invention of the microwave oven

17
Microwaves
  • Your cell phone is actually a radio transmitter
    and receiver that uses microwaves
  • Sends and receives signals from a tower and is
    where the signals come together and allow you to
    connect with other person

18
Infrared Light
  • Found between microwaves and visible light, is
    the type of EM waves most often associated with
    heat
  • You cannot see infrared light, but you can feel
    the results
  • Examples Warming lights at restaurants and your
    toaster

19
Visible Light
  • Part of the EM spectrum that humans can see and
    is the smallest part of the spectrum
  • The longest wavelength is red and the shortest
    is violet
  • The visible light from the sun is white light
    (all wavelengths are combined)

20
Visible Light
  • The range of colors is called the visible
    spectrum

21
Visible Light used in many ways
  • Vision
  • Find food and other survival activities
  • Plants need it to make their food
  • Can you think of anything else?

22
Where does it come from?
  • Most of it comes from the sun
  • The production of light by materials at high
    temperatures is called incandescence
  • Other sources include Lightening and Fire

23
Living things produce light
  • Luminescence is the production of light without
    the high temperatures needed for incandescence.
  • The production of light by living organisms is
    called bioluminescence.
  • Produce by chemical reactions and not intense
    heat
  • Insects, worms, fish, squid, jellyfish, bacteria,
    and fungi

24
Human produced visible light
  • First was fire
  • Electrical lighting in late 1800s (used
    tungsten) was known as incandescent bulbs
  • Fluorescence bulbs
  • Use gas instead of a filament
  • Neon lights (diff gases produce diff colors)
  • LEDs uses a semiconductor that regulates
    electric current to produce light

25
LEDs
  • Light-emitting diodes
  • Idea came from the bioluminescence of animals
  • Light that produces little heat and uses almost
    all of its electrical energy to make light
    instead of the thermal energy
  • Not easily broken

26
Ultraviolet Light (radiation)
  • Has frequencies above those of visible light and
    partially below those of x-rays
  • Carries more energy than visible light
  • Waves can damage skin and eyes (cause sunburn)
  • Used to sterilize medical equipment, kill
    harmful bacteria, produce vitamin D, treat skin
    problems and other medical conditions

27
X-rays
  • Very high frequencies and energy
  • Produced by sun and stars
  • Pass through soft tissue but is absorbed in dense
    matter, like bones
  • Over exposure to x-rays can cause cancer
  • Lead can block these types of EM waves

28
Gamma Rays
  • Highest frequencies and energy of all the EM
    waves
  • Produced by sun and stars and some radioactive
    substances
  • Gamma rays kill normal cells and cause cancer
    cells to develop
  • However, doctors can use gamma rays to kill
    cancer cells and fight tumors when carefully
    controlled

29
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30
Short Story
  • For homework
  • Write a short story in which the characters use
    or are affected by each of the different kinds of
    EM waves
  • Complete on a separate sheet of paper because you
    will turn it in
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