Light

A.  Electromagnetic Radiation (EMR)

1.  The electromagnetic spectrum

a.  Radiation is the transfer of energy by electromagnetic waves.

b.  They do not need a medium to travel through.

c.  They travel at different speeds in different media, but are the fastest waves in nature.

d.  They have different frequencies and wavelengths that give them different properties.

e.  The electromagnetic spectrum (from longest wavelength to shortest):

1)  Radio waves

2)  Infrared radiation

3)  Visible light

4)  Ultraviolet radiation

5)  X Rays

6)  Gamma rays

f.  Photons are tiny packets of radiation of specific amounts of energy that give radiation a particle-like behavior.

2.  Radio waves

a.  Longest wavelength, lowest frequency, and the smallest amount of energy.

b.  Used for radio, television, cellular phones, cordless telephones, radio astronomy, microwaves, RADAR.

c.  Types of radio:

1)  Shortwave (for very long ranges)

2)  AM (amplitude modulation)

a)  Can bend around large objects such as mountains.

b)  AM can reach farther than FM, but is weaker.

c)  Fades out in tunnels.

3)  FM (frequency modulation)

a)  Strong signals anywhere in its range.

b)  Has a range of about 50-70 miles.

4)  Television broadcast waves (FM for sound & AM for picture)

5)  Microwaves

a)  Cause water molecules to vibrate very fast and cook food throughout.

b)  Used for RADAR (Radio Detection and Ranging).

3.  Infrared radiation

a.  Heat

b.  Thermograms show how much infrared radiation is being given off by a living thing.

c.  Used to see things in the dark.

d.  Heat lamps use infrared radiation to heat food.

4.  Visible light

a.  The only part of the electromagnetic spectrum humans can see.

b.  Visible spectrum of color (from longest wavelength to shortest):

1)  Red

2)  Orange

3)  Yellow

4)  Green

5)  Blue

6)  Indigo

7)  Violet

c.  White light is composed of all the colors.

d.  Raindroplets act as little prisms to separate white light into a rainbow of colors.

5.  Ultraviolet radiation

a.  Causes us to make vitamin D in our skin.

b.  Can be harmful.

c.  We use UV to kill germs in food and sterilize medical equipment.

d.  Some minerals glow under UV (used in detergent).

6.  X rays

a.  Their high energy make them pass through many materials.

b.  We commonly use them for X-rays in medicine.

7.  Gamma rays

a.  The most energetic of all EMR.

b.  Used in radiation therapy to kill cancer cells.

B.  Light and Color

1.  Types of materials:

a.  Opaque materials absorb or reflect all light; you cannot see through them.

b.  Transparent materials allow light to pass; you can see clearly through them.

c.  Translucent materials allow only some light to pass through; you cannot see clearly through them

2.  Colors

a.  We see color when materials reflect certain wavelengths of light.

b.  The primary colors are red, green, and blue.

c.  White light is produced when the 3 primary colors are shown together.

d.  How we see color:

1)  Light passes into our eyes and strikes the retina.

2)  Cone cells detect the various wavelengths and send messages to the brain.

3.  Pigments

a.  Pigments are colored materials.

b.  The primary pigments are yellow, magenta, and cyan.

c.  Any other colors can be made from the primary pigments.

d.  Black is produced when the 3 primary pigments are mixed together.

C.  Wave Properties of Light

1.  Reflection

a.  The bouncing off of a wave from an object it strikes.

b.  The law of reflection states that the angle of reflection must equal the angle of incidence.

2.  Refraction

a.  The bending of waves (caused by change in speed).

b.  Light changes speed as it enters or leaves media of different density.

c.  Shorter wavelengths are refracted more.

d.  The sky appears blue because blue is scattered more than other colors and our eyes are most receptive to blue.

3.  Diffraction and Interference

a.  Diffraction is the bending of waves around a barrier.

b.  Longer waves diffract more than shorter waves.

c.  Interference of light by a diffraction grating separates it into its component colors.

d.  Supports the wave theory of the nature of light.