Light Waves - PowerPoint PPT Presentation

All the different colors are electromagnetic waves with different wave lengths

Wave speed = frequency x wavelength

EM radiation is alternating electric and magnetic fields

Changing magnetic/electric field induces electric/magnetic field

Wave speed of light is 300,000,000 m/s

Highest frequencies are violet

The order is red, orange, yellow, green, blue, violet

We shake electrons in an antenna to make radio and TV waves

We shake electrons in a magnetron to make microwaves

We shake electrons in atoms to make light (this is a bit of a simplification which we will correct later this semester

When light strikes a material, it vibrates the lightweight electrons

It will absorb some energy from the EM wave and will vibrate with larger amplitude

It can smack into the electrons in neighboring atoms and vibrate them too

If all the light is absorbed by shaking electrons we say the material is opaque

If the light frequency doesn’t come close to the natural frequencies of the electrons, they shake a bit, but just re-emit the energy

Materials that can’t hold the energy are transparent

This means that the light travels more slowly in these materials!!!

We will use this fact later to do interesting things with lenses

See why the light travels more slowly in a transparent material than in a vacuum?

Microwave EM waves effect the rotation of atoms about each other

+

Remember our discussion of water and how it has a positive end by the hydrogen atoms and a negative end by the oxygen

-

This means that they heat up

Metals are opaque and shiny

The free electrons close to the surface shake and re-emit the energy back out of the material

They are reflectors!!!

The ozone layer absorbs a lot of ultraviolet light

The ozone molecule is O3 and breaks into a regular oxygen molecule O2 and an oxygen atom

Sunlight is a mixture of colors

We call this mixture white light

When white light strikes a red object, the red frequencies are reflected and the other frequencies are absorbed

Black objects absorb all frequencies

Objects can only reflect the colors of light that shine on them

If you shine blue light on a red object it will look black

Filters used on the lights in a theater are materials that absorb some frequencies and let other frequencies pass through

Red filters transmit red light through the material while other frequencies are absorbed

See the discussion on page 289 in the text

Artists have learned how to mix colors to make pleasing combinations and to create a huge array of different colors

All based on what the sensors in our eyes respond to

Red + Blue = Magenta

Red + Green = Yellow

Blue + Green = Cyan

The way your computer screen makes colors. And your TV set does the same thing.

Red + Blue = Magenta

Red + Green = Yellow

Blue + Green = Cyan

Magenta + Green = White

Cyan + Red = White

Yellow + Blue = White

The higher frequencies are scattered more by the molecules in the atmosphere

Reds and oranges just pass through, so the sky appears blue

Sunsets are red!