1. Chapter 27
Properties of Light

2. Light
The two most commonly used models describe light either as a wave or as a stream of particles.
Light produces interference patterns like water waves.
Light can be modeled as a wave.
This model describes light as transverse waves that do not require a medium in which to travel.
Light waves are also called electromagnetic waves because they consist of changing electric and magnetic fields.

5. Electromagnetic Waves
Electromagnetic Waves - energy-carrying waves emitted by vibrating electrons
HowStuffWorks "How Light Works"
Also know as…
Light
Radiation
Photons

6. These three are the same…
Light
pure energy
Electromagnetic Waves
energy-carrying waves emitted by vibrating electrons
Photons
particles of light

8. The Electromagnetic Spectrum
Radio Waves - communication
Microwaves - used to cook
Infrared - “heat waves”
Visible Light - detected by your eyes
Ultraviolet - causes sunburns
X-rays - penetrates tissue
Gamma Rays - most energetic

9. Electromagnetic Wave Velocity
The speed of light is the same for all forms of light.
It is 300,000 kilometers per second or 186,000 miles per second.

10. Speed of Light Speed of light varies with medium.
Light slows down in water
Ex. Straw or spoon appears bent in glass of water

11. The Electromagnetic Spectrum
A range of light waves extending in wavelength from radio waves to gamma rays

13. The Visible Spectrum
A range of light waves extending in wavelength from about 400 to 700 namometers.

14. Transparent Materials
Transparent - the term applied to materials through which light can pass in straight lines

15. Opaque Materials
Opaque - the term applied to materials that absorb light
When the absorption occurs, the vibrations given to the electrons by the light are often great enough to last for awhile, during which the vibratory energy is shared by collisions with neighboring atoms. The absorbed energy warms the material.

16. Reflection
Light may strike a material and bounces off - this is called reflection.
Light shines on metal it sets its free electrons into vibration and the energy is reemitted as visible light.

17. When light is incident upon a material it can behave in three ways:
It can bounce off
It can be transmitted through the material
It can be absorbed by the material
Usually a combination of all three occurs!

18. Transparent/Opaque Is glass transparent or opaque to visible light?
Answer: transparent
Is glass transparent or opaque to ultraviolet light?
Answer: opaque
Atoms give up energy in form of heat as UV light interacts with atoms in the glass. See Figure 27.7
How do UV light bulbs allow UV light transmission?
Answer: made of quartz glass

19. Example Questions Are clouds transparent or opaque to visible light?
Answer: opaque
Are clouds transparent or opaque to ultraviolet light?
Answer: transparent

20. Shadows
Umbra - the darker part of a shadow where all the light is blocked
Penumbra - a partial shadow
These terms also apply to Solar Eclipses and Lunar Eclipses.

21. A solar eclipse occurs when the Moon passes in front of the Sun.

23. A lunar eclipse occurs when the Moon passes into the Earth's shadow.

25. Questions
Which type of eclipse is dangerous to view with the unprotected eye?
Why are lunar eclipses more commonly seen than solar eclipses?
Lab 70 “Shady Business”

26. SEEING LIGHT – PARTS OF THE EYE
Cornea -
does most of the focusing
Iris -
has the eye color and controls light intensity
Pupil -
the hole in the eye
Lens -
does remainder of focusing
Retina -
location of light sensors, has rods and cones
Fovea -
center of vision, predominantly cones
Blind spot -
optic nerve exit, no light sensors

27. Parts of the Eye Detectors on the Fovea
Rods
light intensity sensitive
Cones
color sensitive
The blind spot for the eye is cause by the optic nerve.

28. Color Deficiency

29. Myopia (Near-Sightedness)
People with near-sightedness cannot see clearly at distance.

30. Hyperopia (Farsightedness)
People with far-sightedness cannot see clearly up close.

31. Doppler Effect and Expanding Universe
Doppler effect also occurs for light waves from stars and galaxies.
When a light source approaches earth there is an increase in its frequency – called “blue shift”
When a light source goes away from earth there is a decrease in its frequency – called “red shift”

32. Polarized Light and 3-D
Polarizing filters transmit parts of incident nonpolarized light that are parallel to the polarization axis, and block components vibrating at right angles to the polarization axis. Emergence of polarized light.
Lab 72 “Shades”
There are a variety of 3-D viewing techniques, all of which involve each eye seeing a different view – binocular vision.