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Chapter 17: Electromagnetic waves. 17.1: Electromagnetic waves have unique traits. Electromagnetic waves: A disturbance that transfers energy through a field. Also called EM waves Most are invisible Field:

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17 1 electromagnetic waves have unique traits
17.1: Electromagnetic waves have unique traits
  • Electromagnetic waves:
    • A disturbance that transfers energy through a field.
    • Also called EM waves
    • Most are invisible
  • Field:
    • An area around an object where the object can apply a force (push or pull) to another object without touching it
field example
Field example

Electric Force Fields

how em waves form
How EM waves form

Occur when electrically charged atomic particles move

The charged particles exert an electric force on each other (electric field)

A moving charged particle also creates a magnetic force thus creating a magnetic field

Quickly moving charged particles vibrate at right angles to each other

sources of em waves
Sources of EM waves

Most of our EM waves come from the sun

Technology has given us the ability to create EM waves on our own for various uses

em waves can travel in a vacuum
EM waves can travel in a vacuum
  • Radiation:
    • Energy that moves in the form of EM waves
  • Different from mechanical waves:
    • EM waves can travel through a vacuum or space with no matter which means it does not lose energy as it moves
    • Mechanical waves must vibrate the medium they travel through using some of the wave’s energy
speed of em waves
Speed of EM waves
  • In a vacuum EM waves:
    • Travel at a constant speed
    • 186,000 mi/s (300,000 km/s) AKA speed of light
    • At this speed, rays from the sun take approximately 8 minutes to reach the earth
em waves can interact with a material medium
EM waves can interact with a material medium
  • Energy can be transferred, reflected, refracted, or diffracted which causes a change in direction of the EM wave.
  • Transferring energy:
    • Moves potential energy from one place to another
    • Converts potential energy into kinetic energy by moving the medium back and forth
17 2 electromagnetic waves have many uses
17.2: Electromagnetic waves have many uses
  • Frequencies:
    • Determines the wave’s characteristics and uses
    • Higher frequency EM waves have more vibrations per second and more energy
    • Lower frequency EM waves have longer wavelengths and less energy
electromagnetic spectrum
Electromagnetic spectrum
  • The range of all EM frequencies
  • Broken up to represent 7 parts of the spectrum by frequency from low to high (right to left)
  • Some areas of the spectrum overlap
  • Frequency is measured in hertz (Hz)
    • 1 Hz = 1 cycle per second
radio waves
Radio waves

EM waves that have the longest wavelength, lowest frequency, and lowest energy

Easily pass through the atmosphere and other materials

AM: amplitude modulation

FM: frequency modulation

microwaves
Microwaves
  • Shorter wavelength, higher frequencies, and higher energy than radio waves
  • Radar
    • Radio detection and ranging
    • Used to detect the position of an object
  • Cell phone:
    • Radio transmitter and receiver that uses microwaves
visible light
Visible Light
  • What the human eye can see
  • Range is between 1014 Hz and 1015 Hz
  • Longest wavelength is seen as red

Picture of visible light spectrum

  • Shortest wavelength is seen as violet
infrared light
Infrared Light
  • Found between microwaves and visible light
  • Generally associated with heat (heat rays)
  • Can not see infrared rays but you can feel them
    • Heat from the sun, fire, heat lamps
  • Some animals can see infrared light (pit viper snakes)
ultraviolet light
Ultraviolet Light

Frequencies above those of visible light and partially below x-ray

Carries more energy than visible light

Causes damage to your skin and eyes

Causes your skin to produce vitamin D

Can be used to sterilize equipment and food

Bees and other insects can see higher frequencies allowing them to see “nectar guides” on flowers

x rays
X-rays

Very high frequency and energy

Produced by the sun and technology

Can pass easily through the soft tissues of the body but are absorbed by bone

Blocked by lead

gamma rays
Gamma rays

Highest frequency and energy—lowest wavelength

Produced by radioactive substances, the sun, other stars

Can penetrate the soft and hard tissues of the body-kills normal cells—causes cancer to develop

Used as radiation treatment of cancer in some patients

17 3 the sun is the source of most visible light
17.3: The Sun is the source of most visible light.
  • Incandescence:
    • The production of light by materials at high temperatures
    • Glows or bursts into flames
    • Lightning
    • Light bulbs
    • fire
slide21

Luminescence:

    • Production of light without the high temperature
  • Bioluminescence:
    • Production of light by living organisms
    • Produce light by chemical reactions inside an organism’s tissues
    • firefly
incandescent and fluorescent lighting
Incandescent and Fluorescent Lighting
  • Light bulbs:
    • Sealed glass tube with a thin tungsten wire (filament)
    • Tungsten gives off bright light when heated
    • Wasteful in terms of energy by giving off a lot of heat in the form of infrared radiation
slide23

Fluorescence:

    • When a material absorbs EM radiation of one wavelength and gives off EM radiation of another
    • Bulb filled with a mixture of mercury vapor and other gases that give off UV light when electric current passes through
    • Inside of the bulb is coated with phosphor powder
    • More energy efficient and economical
slide24

LEDs

    • Light emitting diode
    • Semiconductor which regulates the electric current by converting electric energy directly into visible light
    • Produce very bright light with little energy-produce little heat
17 4 light waves interact with materials
17.4: Light waves interact with materials
  • Transmission:
    • Passage of EM waves through a medium
    • If light was not reflected by objects, we would not see most of the objects.
  • Absorption:
    • Disappearance of EM waves into the medium
    • Affects how things look by limiting the light available to be reflected or transmitted
how materials transmit light
How materials transmit light
  • Transparent:
    • Allows most of the light that strikes them to pass through
    • You can see objects through a transparent material
    • Air, glass, sandwich bags
  • Translucent:
    • Materials transmit some light
    • Cause light to spread out in all directions
    • You can see light through translucent materials but not objects (clearly)
    • Notebook paper
slide27

Opaque:

    • Material that does not allow any light to pass through
    • They either reflect light, absorb light, or do both
    • Wood, rocks, ceramic mugs
  • Scattering:
    • The spreading out of light rays in all directions
    • Particles reflect and absorb the light
    • Creates glare
    • Making the light brighter causes more scattering
slide28

Scattering cont.

  • Scattering is what makes the sky blue:
    • The blue part of the visible spectrum is scattered more easily than the other colors.
    • When the sun is setting, the blues and greens have been scattered leaving the reds and oranges in the sunset
  • Polarization:
    • Quality of light where all wavelengths vibrate in the same direction
    • Waves traveling in other directions are filtered out
wavelengths determine color
Wavelengths determine color
  • When all wavelengths are present together the light appears white.
  • Prism:
    • A tool that uses refraction to spread out the different wavelengths that make up white light.
color reflection and absorption
Color reflection and absorption
  • The color of an object or material is determined by the wavelengths absorbed and reflected
  • An object is the color of the wavelengths it reflects:
    • White objects reflect ALL wavelengths
    • Black objects absorb ALL wavelengths
    • Green limes absorb all wavelengths except green which is reflected
primary colors
Primary colors:
  • Three colors of light which can be mixed to produce all possible colors
    • Red
    • Blue
    • Green
  • These three color bands are the only ones the human eye can detect
  • When equally mixed, white (colorless) is produced
primary pigments
Primary pigments
  • Pigment:
    • A material that is used to produce colors
  • Primary pigments:
    • Cyan
    • Yellow
    • Magenta
  • When mixed together in equal amounts, black is produced