Light

I.	Electromagnetic spectrum
A.	Electromagnetic waves are transverse waves produced by the motion of electrically charged particles
1.	How light travels
2.	Speed of light
a.	Measured by Danish astronomer Olaus Roimer . 
b.	300 million meters Isecond 3 x 108 mls c. 7.5 times around the earth in 1 second
B.	Describing the Electromagnetic Spectrum
1.	They all travel the same speed
2.	Have different wave lengths and frequencies 3. They are particle like bundles of energy called photons
C.	The different wavelengths of the spectra
1.	Radio waves
a.	Low energy and low frequency waves
b.	AM are the longest and lowest frequency waves
1)	Amplitude modulaton
2)	535 kiloHz to 1605 kiloHz
c.	FM
1)	Frequency Modulation
2)	88 mega Hz to 107.9 megaHz
d.	Microwaves are the shortest wave (Highest frequency) Radio wave
1)	Used for transmitting telephone Messages 
2)	Cooking food.
2.	Infrared Radiation
a.	All objects give off some infrared radiation
b.	Used to warm food
c.	Used in thermograms
d.	Used to track things in fog in darkness
3.	Visible light
a.	The small portion of the radiation that we can see
b.	From Red to Violet
4.	Ultraviolet Radiation
a.	Wavelength just shorter than visible light
b.	Present in the sunlight and causes the skin to tan and to burn
c.	Cause skin cells to manufacture vitamin
d.	Over exposure kills cells
e.	Used to kill bacteria in sterile rooms
f.	Wear protected from harmful Ultra Violet radiation from the sun by the ozone layer
5.	X-rays
a.	High Frequency electromagnetic waves that are produced when high energy electrons are passed through a tube and hit a target
b.	X-rays go through most matter
1)	Concrete and lead slow it down
c.	Called X-ray because the source of film exposure was not originally known.
6.	Gamma rays have the highest frequency and the most penetrating of all the electromagnetic waves
II.	Light & Color A. Light and matter
A.	Materials
1.	Opaque materials are materials that absorb or reflect light
2.	Translucent materials are materials that let some light through but you can't see clearly through it
3.	Transparent means allows light to pass through so that you can see clearly through it
B.	Colors are the result of materials ability to absorb and reflect different light spectra
C.	There are three primary colors of light
1.	Red
2.	Green
3.	Blue
D.	Vision and seeing color
1.	We have cones in out eyes that see red green and blue
a.	When the colors are focused on our retina we are able to see things in the right shape and color
b.	Color Blindness is the lack of the proper cones in your eye
2.	Pigmentation and the primary colors
a.	Red
b.	Yellow
c.	Blue
3.	Brightness of light
a.	SI unit of brightness is the lux
b.	1000 lux is needed for comfortable reading
1)	0.2 joules of light energy/second
c.	The energy of the lux depends on the color of the light

LIGHT: Particles or Waves?
•	Wave Model of Light
–	Explains most properties of light
•	Particle Theory of Light
–	Photoelectric Effect – Photons of light produce free electrons
Color of Light
•	Transparent Objects: 
–	Light transmitted because of no scattering
–	Color transmitted is color you see.  All other colors are absorbed.
•	Translucent: 
–	Light is scattered and transmitted some.
•	Opaque: 
–	Light is either reflected or absorbed.  
–	Color of opaque objects is color it reflects.
Color of Light
•	Color of Objects
–	White light is the presence of ALL the colors of the visible spectrum.
–	Black objects absorb ALL the colors and no light is reflected back.
Color of Light 
•	Primary Colors of Light
–	Three colors that can be mixed to 
  produce any other colored light
–	Red + blue + green = white light
•	Complimentary Colors of Light
–	Two complimentary colors combine 
  to make white light-Magenta,Cyan,Yellow
LIGHT: Refraction of Light
•	Refraction – Bending of light due to a change in speed.  
–	Index of Refraction – Amount by which a material refracts light.
–	Prisms – Glass that bends light.  Different frequencies are bent different amounts & light is broken out into different colors.
Refraction
The Human Eye
How You See
•	Retina – 
–	 Lens refracts light to converge on the retina.  Nerves transmit the image
•	Rods – 
–	Nerve cells in the retina.  Very sensitive to light & dark
•	Cones – 
–	Nerve cells help to see light/color
How You See 
•	Near Sighted – Eyeball is too long and image focuses in front of the retina
•	Far Sighted – Eyeball is too short so image is focused behind the retina.

Paint Pigments
–	Pigments absorb the frequency of 
	light that you see

–	Primary pigments
•	Yellow + cyan + magenta = black
•	Primary pigments are compliments 
	of the primary colors of light.
Complementary Pigments 
•	Green, blue, red
•	Complimentary pigments are primary colors for light!

Reflection 
•	Reflection – Bouncing back of light waves
–	Regular reflection – mirrors smooth surfaces scatter light very little.  Images are clear & exact.
–	Diffuse reflection – reflected light is scattered due to an irregular surface.
Mirrors
•	Plane Mirrors – Perfectly flat
–	Virtual – Image is “Not Real” because it cannot be projected
Mirrors
•	Reflection & Mirrors (Cont.)
–	Convex Mirror
•	Curves outward
•	Enlarges images.
–	Use:  Rear view mirrors, store security…
Lenses
•	Convex Lenses 
–	Thicker in the center than edges.  
–	Lens that converges (brings together) light rays.  
–	Forms real images and virtual images depending on position of the object
Lenses
•	Convex Lenses 
•	Ray Tracing
–	Two rays usually define an image
•	Ray #1:  Light ray comes from top of object; travels parallel to optic axis; bends thru focal point.
Lenses
•	Convex Lenses 
•	Ray Tracing
–	Two rays define an image
•	Ray 2:  Light ray comes from top of object & travels through center of lens.
Lenses
•	Concave Lenses – 
–	Lens that is thicker at the edges and thinner in the center. 
–	Diverges light rays 
–	All images are erect and reduced.
Lenses
•	Concave Lenses – 
–	Vision – Eye is a convex lens.
•	Nearsightedness – Concave lenses expand focal lengths
•	Farsightedness – Convex lenses shortens the focal length.
Optical Instruments
•	Cameras
•	Telescopes
•	Microscopes
Optical Instruments
•	LASERS
–	Acronym: Light Amplification by Stimulated Emission of Radiation
–	Coherent Light – Waves are in phase so it is VERY powerful & VERY intense. 
Optical Instruments
•	LASERS
–	Holography – Use of Lasers to create 3-D images
–	Fiber Optics – Light energy transferred through long, flexible fibers of glass/plastic
–	Uses – Communications, medicine, t.v. transmission, data processing.
Diffraction
•	Diffraction – Bending of waves around the edge of a barrier.  New waves are formed from the original. breaks images into bands of light & dark and colors. 
•	Refraction – Bending of waves due to a change in speed through an object. 
Diffraction 
•	A diffraction grating.  Each space between the ruled grooves acts as a slit.  The light bends around the edges and gets refracted.
Light & Color 
•	Light and matter
•	Materials
–	 Opaque materials are materials that absorb or reflect light
–	 Translucent materials are materials that let some light through but you can't see clearly through it
–	 Transparent means allows light to pass through so that you can see clearly through it

 Vision and seeing color
•	 We have cones in out eyes that see red green and blue
–	 When the colors are focused on our retina we are able to see things in the right shape and color
–	 Color Blindness is the lack of the proper cones in your eye

Brightness of light

a.     SI unit of brightness is the lux
b.     1000 lux is needed for comfortable reading
1)   0.2 joules of light energy/second
c.     The energy of the lux depends on the color of the light

 Models of light

A.  Isaac Newton 1672 said that light is a steam of tiny particles
B.  Christian Huygen found that light is a wave, because one beam of light can pass through another without disturbance
C.  Thomas Young in 1804 showed that light has constructive and destructive interference which proved it to be a wave
D.  Albert Einstein in 1905 said that energy form light comes out in tiny packages of energy called photons
E.   It is now known that light is photons that travel in a wave pattern