1. Chapter 16
light

2. Light –can be explained in terms of particles AND waves
Light travels in a straight line in a vacuum or other uniform medium. This straight line model is the RAY MODEL and helps to explain reflection and refraction.
It acts like a wave.
Acts like particles because it can diffract and constructively and destructively interfere.

3. Light is the Range of frequencies of electromagnetic waves that stimulate the retina
The color of the objects that we see are largely due to the way
those objects interact with light and
ultimately reflect or transmit it to our eyes.
The color of an object is not actually within the object itself.
Rather, the color is in the light that shines upon it and is
ultimately reflected or transmitted to our eyes

4. .
Unlike the mechanical waves we have looked at - energy of an electromagnetic wave energy is directly related to its frequency, therefore higher frequency (shorter wavelength) EM waves have more energy than lower frequency (longer wavelength) EM waves.
Light waves have wavelengths from about 4 X ( 400 nanometers) to 7 X meters (700 nanometers)
The longest to shortest are ROY G BIV

5. Speed of light in a vacuum is _____
The symbol for this speed is _
Formula for speed of light is v = λf .
Light travels at different speeds in different mediums.
If a problem does not give you a medium that light is traveling in – use speed of light in a vacuum.
Use your reference table to find frequency and wavelength ranges.

6. v = λf where v = speed of light in a vacuum
Use your reference tables for wavelengths of light and electromagnetic waves.
v = λf where v = speed of light in a vacuum
Orange light has a frequency of 5.0 x 1014 hertz in a vacuum. What is the wavelength of this light?
2. How much time does it take light from a flash camera to reach a subject 6.0 meters across a room?
3. In a vacuum, light with a frequency of 6.0 x 1014 hertz has a wavelength of_________________ What color would it be?
Also wavelength of max absorption of a cockroach 4. Electromagnetic radiation having a wavelength of 1.3 x 10-7 meter would be classified as
a)infrared
b)ultraviolet
c)orange
d)blue

7. Chap 17 Reflection and Refraction
LAW OF REFLECTION: The angle that an incoming light beam makes with the normal line, called the angle of incidence, is equal to the the angle of the outgoing beam, called the angle of reflection.

8. Which one of the angles (A, B, C, or D)
Consider the diagram.
Which one of the angles (A, B, C, or D)
is the angle of incidence? ______
Which one of the angles is the angle of reflection? ______

9. A ray of light is incident towards a plane mirror
at an angle of 30-degrees with the mirror surface.
What will be the angle of reflection?

10. Why then do some surfaces give
a clear image and some give a blurred vision?

11. Refraction – change in direction or
bending of a wave at the boundary between two media
as it goes into the second media.
Ex:

12. AS a light beam enters another media,
the initial beam is called the INCIDENT RAY
and the beam in the second media is called the REFRACTED RAY.
ANGLE OF REFRACTION
angle which the refracted ray makes with the normal line at the surface.

15. If the refracted ray is SMALLER than the angle of incidence, the new media is more OPTICALLY DENSE and the speed of light will be SLOWER
Example; Light going from air into water
If it is LARGER than the angle of incidence, then the new media is less OPTICALLY DENSE and the speed of light will be FASTER.
Example light going from water into air
Medium is what material light is travelling through
What happens in the following pictures? How would we draw the refracted ray?

16. where ("theta i") = angle of incidence
("theta r") = angle of refraction
ni = index of refraction of the incident medium
nr = index of refraction of the refractive medium
SNELL’S LAW

17. When light goes from one medium to another it may refract and reflect
When light goes from one medium to another it may refract and reflect. The degree to which it bends depends on the angle of incidence and the properties of the medium. There is an established INDEX OF REFRACTION for different media. See REFERENCE TABLE:
What is it for water?
Diamond?
Lucite?
What does it really Mean???
Really it is a ratio of n = speed of light in a vacuum
speed of light in a medium

18. In the following two examples, use Snell's law, the sine button on your calculator, a protractor, and the index of refraction values to complete the following diagrams. Measure , calculate , and draw in the refracted ray with the calculated angle of refraction.

19. What is the angle of refraction?
A ray of light passes from air into a sheet of crown glass at 30°.
What is the angle of refraction?
Draw the rays of incidence and refraction and label them and the 2 media.

20. Light in air is incident upon a piece of crown glass at an angle of 45°. What is the angle of refraction? Draw the rays of incidence and refraction at the proper angles and label them and the 2 media.

21. An unknown material block is submerged in water.
Light in the water is incident on the block at 31° and it refracts at 27° in the material.
What is the index of refraction of the unknown block?
What material might it be?
Draw the problem with accompanying rays and angles drawn.

22. There is a CRITICAL ANGLE
There is a CRITICAL ANGLE. This is when the angle of incidence produces a
refraction angle of 90° as it enters a new medium.
REMEMBERTHIS **********
What might this be for water into air?
When light strikes a surface along the perpendicular, the angle of incidence is zero and refraction is zero.

23. SPEED of LIGHT changes in different media.
FORMULA: n = c/v
How are they related??
n= sine Φi / sine Φr
Where Φi = angle of incidence
Φr = angle of refraction
Just as angles change the speed of light in a medium changes
n = index of refraction
c = speed of light ( on reference table) 3 X 108 m/s
v = calculated speed of light in a medium
n = c/v
Find the speed of light in water.
n in water =
c = 3 X 108 m/s
v = ?
As Speed changes, wavelength changes:n2/n1 = v1/v2 = λ1/λ2
Another forgotten relationship. ON REFERENCE TABLE

24. A ray of light incident upon a mirror
makes an angle of 36° with the mirror.
What is the angle between the incident ray and the reflected ray? Draw the diagram

25. A ray of light has an angle of incidence of 30° on a block of quartz and an angle of refraction of 20°. What is the index of refraction for this block of quartz?

26. A ray of light is incident at an angle of 60°
upon the surface of a piece of crown glass. What is the angle of refraction?

27. What is the speed of light in a diamond?

28. The speed of light in chloroform
is 1.99 X 108 m/s.
What is the index of refraction?

29. Energy of an EM Wave - Reminder
The electromagnetic spectrum describes the types
of electromagnetic waves observed
at the specified frequencies and wavelength.
It is also important to note that the energy of an
electromagnetic wave is directly related to its frequency,
therefore higher frequency (shorter wavelength)
EM waves have more energy than
lower frequency (longer wavelength) EM waves.
Formula is E = hf
Where E is energy in Joules
h = Planck’s constant or 6.63 X 10 ^-34 J*s
f = frequency
An x-ray, therefore, has considerably more energy than
an AM radio wave! Using the diagram, more energetic waves
are shown on the left of the EM Spectrum diagram, and less energetic waves
are shown to
the right on the EM Spectrum. We'll explore the energy of EM radiation
further in our Modern Physics unit.

30. Polarization of Light – What is it? Why is it useful?

31. Light shining through a prism will be separated into its different wavelengths The separation of visible light into its different colors is known as dispersion. Each color is characteristic of a distinct wavelength; and different wavelengths of light waves will bend varying amounts upon passage through a prism. For these reasons, visible light is dispersed upon passage through a prism.
White is the combination of all the colors of the visible light spectrum. If all the wavelengths of the visible light spectrum give the appearance of white, then none of the wavelengths would lead to the appearance of black. Once more, black is not actually a color. Technically speaking, black is merely the absence of the wavelengths of the visible light spectrum

32. What do these mean? Critical Angle Diffusion Dispersion Polarized
Reflection
Refraction
Total Internal reflection
Energy of sound wave is related to WHAT?
Energy of electromagnetic wave is related to WHAT?
What happens to electromagnetic waves as they change media?

33. Total Internal Reflection
When light passes from a More Optically Dense medium to a Less Optically dense medium at an angle so great there IS NO REFRACTED RAY of LIGHT =
Total Internal Reflection.
To know when this would occur, you solve using Snell’s Law where you know ANGLE of REFRACTION = 90 degrees or is called the CRITICAL ANGLE. Any angle GREATER than the critical angle will result in TOTAL INTERNAL REFLECTION>
Ex: Solve for incidence angle for a light ray going from water into air that would be totally internally reflected.
DISPERSION = separation of light into its spectrum.
LIGHT DIFFRACTION – light passing through 2 slits diffracts like a wave. It has constructive and destructive interference. Constructive interference leads to bright bands of color and destructive interference leads to light bands or dark areas.