1. Light Waves Interacting with Matter
(Chapter 7)
Student Learning Objective
Determine the behavior of electromagnetic waves as they interact with different types of matter.

2. What determines how light will interact with matter?
Light interacts differently with different types of matter.
Surface
Material
Angle of incidence
Wavelength
Opaque materials absorb (Blacktop) or reflect light.
These Practice Problems are presented in class

3. Light is able to travel through transparent materials. (Transmission)
Light may be absorbed and re-emitted.
Light may pass through the material.
Speed changes
Air & Glass
If SuperPowers Were Real: Invisibility

4. What is the law of reflection?
Reflection occurs when light bounces from a surface back into the original medium.
Law of Reflection:
Incoming light rays and outgoing light rays have the same angle with respect to the normal line.
The law of reflection applies to all reflective surfaces. I R
Mirror

5. Diffuse Reflection Practice: Does the law of reflection apply to diffuse reflection?
A flat mirror reflects all light rays in the same direction.
Upright
Same size
Same distance
Left-right reversed

6. Photo Source: Copyright © Bobby H. Bammel. All rights reserved.
Reflected Light
It is the reflection of light that allows us to see things and in places where direct light does not hit – in the shadows!
Photo Source: Copyright © Bobby H. Bammel. All rights reserved.
Section 7.1

7. For a person to see her/his complete figure in a plane mirror, the height of the mirror must be at least one half the person’s height.
Section 7.1

8. Curved Mirrors Convex mirrors always produce a smaller image.
Curved Mirrors
Convex mirrors always produce a smaller image.
Concave mirrors usually produce a larger image.

9. Practice
These Practice Problems are presented in class

10. When and how is light refracted?
Light will change speed and may change direction when it is transmitted from one material to another. (Refraction)
 Properties Affect Refraction
Wavelength
Angle of incidence
Material (n = c/v)
Temperature
Why is glass transparent? - Mark Miodownik

11. Refraction affects where objects appear to be.
The change in index of refraction determines the direction light “bends”.
Low to high n  light bends toward
normal line
High to low n  light bends away
from normal line
Refraction affects where objects appear to be.
(1:14)

12. Indexes of Refraction for Common Substances
The higher the Index of Refraction (n) the more the light slows.
Section 7.2

13. Practice
These Practice Problems are presented in class
𝑛= 𝑐 𝑣

14. When does total internal reflection occur?
Total internal reflection occurs when light approaches a boundary at the critical angle.
The critical angle is the angle at which the material reflects the light ray and does not allow transmission.

15. Internal Reflection Exceeding the Critical Angle (qc)
Diamonds and other gemstones are facetted in such a way to enhance internal reflection.
Fiber-optics – used to “pipe” light down and back along glass/plastic fibers
Section 7.2

16. How is a rainbow formed?
Dispersion occurs when visible light is divided into separate colors.
Each person sees their own set of colors (rainbow) from a particular set of raindrops.

17. Practice
These Practice Problems are presented in class

18. Line Spectra Each line spectrum is unique to a specific element.
Deadliest Colors
Section 7.2

19. What do lenses do to light?
Refraction
Convex Lens
(true image)
Concave Lens
(virtual image)
Question: What type of lens is the human eye?

20. What is polarized light?
Light is many transverse waves vibrating in many directions.
Polarized light has only one direction of vibration.

21. What causes diffraction?
These Practice Problems are presented in class
What causes diffraction?
Diffraction occurs when light waves bend around corners.
The amount of diffraction depends on the how the size of the wavelength compares to the size of the barrier.
Shadows

22. How are colors produced?
Most of the colors you see in the world are due to selective reflection.
Practice
These Practice Problems are presented in class

23. The Earth appears blue because blue (and violet) photons are scattered as they collide with atoms and molecules within the air.
The sky on Earth appears red at sunset because the light must pass through a lot of atmosphere.

24. Practice
These Practice Problems are presented in class

25. Some objects have a particular color because of temperature.
Wavelength of Maximum Emission:
Every object has a specific wavelength (color) at which it radiates most of its energy.
T(Kelvin) = 3,000,000
lmax (nm)

26. Practice
These Practice Problems are presented in class