LIGHT &

APPLICATIONS OF OPTICS

Light

Light interacts with matter in 4 known ways.

It sometimes bounces off matter. Sometimes it is absorbed by matter. In some cases it passes through the matter. Most times it bends as it encounters matter. *

What is Light?

Light is energy and travels in the form of a wave. We call them electromagnetic waves.

Light travels in straight lines unless another force acts upon it.

Electromagnetic Waves

Waves that carry electrical energy and magnetic energy.

An important characteristic of a wave is it’s wavelength. The wavelength of a wave is the distance between two peaks. It also determines the color of the light.

Types of Light Emission

Incandescence Light given off by an object because it is very hot. Ex. incandescent light bulb (old style light bulb, very

inefficient, 90% heat, 10% light, filament 3000°C)

Luminescence

Light given off by an object that has not been heated.

Chemiluminescence is light that is release during chemical reactions Ex. glow sticks Bioluminescence Is a form of Chemiluminescence that occurs in living

organisms. Ex. fireflies

Electrical Discharge

occurs in a sealed glass tube containing one or more gases.

Electricity travels from one end to the other bumping into particles of gas, giving them energy.

The gases release this energy as light. Ex. street lights

Fluorescence

is a form of electric discharge. But these gases emit ultraviolet light.

the walls of the glass tube are covered with a substance called a phosphor.

The ultraviolet light transfers energy to the phosphor, which then releases the energy as light

Ex. lights in the ceiling

Electromagnetic Spectrum

a representation of the types of electromagnetic waves arranged according to wavelength

The only waves of the electromagnetic spectrum that you can see are those of visible light.

The longest waves of visible light are red and the shortest are violet.

Behavior of Light

Reflection the process in which light "bounces off“ the surface

of an object and travels in another directionAbsorption the process in which light energy remains in the

object that it hits, and the light energy is converted into heat

Transmission the process in which light travels through an object

and continues travelling

Properties of Matter wrt Light

Transparent A property of an object that allows light to

penetrate it, making it possible to see objects from the other side.

Translucent A property of an object that allows light to pass

through but scatters it in different directions.Opaque A property of an object that will not allow any light

to penetrate it.

Color of Opaque Objects

The color of opaque objects depends on what light they reflect.

White objects reflect all colors of the visible spectrum.

Black objects absorb all colors of the visible spectrum.

Blue objects absorb all colors except blue. Some objects reflect mostly one color but a little of

some others creating shades of a color.

Color of Translucent or Transparent Objects

For a transparent or translucent object to have a certain color, it must absorb all other colors of light

It must also transmit and reflect the color that is its particular color.

Color

Additive Primary Colors to add colors, you need sources of colored lights

that can reach an observer's eyes.

primary additive colors are red, green and blue

overlapping all 3 produces white

overlapping 2 produces secondary colors

secondary additive colors are cyan, magenta and yellow

Red + Green = YellowRed + Blue = MagentaGreen + Blue = Cyan

*

Subtractive Primary Colors when an object absorbs a color, it removes it from

the beam of light or subtracts it Most of the color we see is the result of subtractive

colors. primary subtractive colors are cyan, magenta and

yellow. overlapping all 3 produces the color black

subtracting equal amounts of two of the three subtractive primary colors make secondary colors

secondary subtractive colors are the same as the primary additive colors, Red, Green and Blue

White – (Cyan + Magenta) = BlueWhite – (Cyan + Yellow) = Green

White – (Magenta + Yellow) = Red*