Shedding some light on…...

….light!!!!(or “light conversation”)

Let’s Review:

• Light can be modeled three ways:

1. As a ray1. As a ray

2. As a wave2. As a wave

3. As a particle(photon)3. As a particle(photon)

The Ray model:

• A ray is a line that goes forever

• It is useful for diagramming where the light goes

What stations are best explained with the ray model of light?

Rays & the rules of Reflection

Rays are like a basketball bounce pass: The angle of the pass is equal to the angle of bounce:

passpass bouncebounce

Pass= angle of incidence link

Bounce= angle of reflection

….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”

Fiber Optics and T.I.R.

• Light reflects inside (internally) the fiber optics and makes it to other side.

Known as “Total Internal Reflection”

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:

Remember the coin trick??

Diagram it now, using the “line of sight rule”

What about those upside down periscope images we saw???

Use the ray model and the rule about mirror reflection to diagram

this….

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??

Three things light can do:

• Get Reflected: “Bounced off”

• Get Absorbed: “Soaked in”

• Get Transmitted: “Passed through”

• These have a huge impact on color.

The ““jello-man®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.

Link

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.

Wave or Particle???!!!???

• Waves aren’t particles, particles aren’t waves…. So why two models?

• First, a little story about an experiment...

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)

WAVES

wavelength

crestamplitude

trough

Wave characteristicsWavelength affects color

Amplitude affects brightness

Frequency is how often a part of wave hits per second

(hertz= 1/sec.)