2. Let’s Review:
• Light can be modeled three ways:
1. As a ray
2. As a wave
3. As a particle(photon)
3. The Ray model:
• A ray is a line What stations are
that goes best explained
forever with the ray
model of light?
• It is useful for
diagramming
where the light
goes
4. Rays & the rules of Reflection
Rays are like a basketball bounce pass: The
angle of the pass is equal to the angle of
bounce:
pass bounce
Pass= angle of incidence link
Bounce= angle of reflection
5. ….unless of course the floor is
bumpy…
(this is a surface that is NOT a mirror)
the rays go all over the place:
this is called diffuse reflection
Diffuse means “scattered”
6. Fiber Optics and T.I.R.
• Light reflects inside (internally) the fiber
optics and makes it to other side.
Known as “Total
Internal
Reflection”
7. Rays & the “line of sight” rule
Your eye sees things as where they came
from. The dog looks like its “in” the mirror
Mirror:
link
eye:
8. Remember the coin trick??
Diagram it now, using the
“line of sight rule”
9. What about those upside down
periscope images we saw???
Use the ray model and the rule
about mirror reflection to diagram
this….
10. Light is a wave:
• Energy often travels in waves, and
light is energy!!!
• When wavelength (λ) changes, the
color changes.
• Wavelength is a measurement.
• What is the wave model used to
explain??
11. Three things light can do:
• Get Reflected: “Bounced off”
• Get Absorbed: “Soaked in”
• Get Transmitted: “Passed through”
• These have a huge impact on color.
12. The “jello-man®” trick….
..To figure out which way a ray will refract.
1. Draw the light ray until it encounters a new
medium (like hitting the jello)
2. Figure out if this new medium slows down
the light or not
3. Put “arms” on the ray.
4. Whichever arm is stuck in the slower
medium is the direction light will bend.
14. Light as a particle
• Einstein discovered, using special
equipment, that light acts like tiny
bullets.
• He called them photons.
• When they encounter metal, these
photons cause electrons to fly off the
metal surface.
15. Wave or Particle???!!!???
• Waves aren’t particles, particles aren’t
waves…. So why two models?
• First, a little story about an
experiment...
16. The “double slit” experiment
• Pass light through two thin slits
• The waves emerge on the other side in
a pattern like waves in water would
• The two sets of waves interact 2 ways:
– waves cancel each other(destructive
interference)
– waves amplify each other(constructive
interference)
