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REFRACTION

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168C: Think About It

  • A car speeds along a highway and suddenly hits the soft shoulder on the side of the road.
    • What happens to the front right tire that hits the soft shoulder?

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    • As a result, what happens to the car?

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168C: BENDING LIGHT RAYS

  • Light travels in straight lines, at a constant speed, as long as it is moving through one medium
  • When light passes from one medium to another, the denser medium slows light down
    • Just like when the car slows down when rolling on gravel, light traveling from air to water will slow down since water is more dense than air
  • Refraction: bending of light as it travels from one medium to another

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168C: REFRACTION IN REAL LIFE

  • Demo

https://www.youtube.com/watch?v=95V-QJYZ2Dw

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  • Why does the popsicle stick look bent in the glass of water?

Because ….

The light hits the water and ___________, so it refracts!

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168C: LAB TIME! “Refraction Lab”

Materials: Beaker, test tube (glass), test tube tongs, oil, Notebook (for observations and appearances, and to answer questions) Safety: glass breaks (I will clean), oil - don’t spill,Instructions:

  1. Get 1x paper towels, 1x beaker with oil, 1x tong, 1x test tube
  2. Make observations: Describe the appearance of the test tube. Put it near your eye & look through it. How do images on the other side appear? List at least 3 qualities.
  3. Put empty test tube in oil (don’t submerge it). How does the test tube appear?
  4. Submerge the test tube. Let it fill with oil. Describe the appearance
  5. Why did the test tube do that? What was different between the tube with oil inside & without oil inside?

CLEAN UP:

  1. Use a paper towel to wipe off the outside of the beaker and your desk.
  2. Pour the oil in the test tube back into the beaker. Dry the outside of the test tube with a paper towel. Inside of tube too (if you can)
  3. Dry the end of the tongs
  4. Throw away the towel. Put everything back where you found it.

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158C: “REFRACTION IN REAL LIFE”

  • A Touch of Glass

https://www.youtube.com/watch?v=OZxtwIc3ieM

  • Sketch an image of the experiment, including the path of a light ray traveling from the opposite side of the beaker, through the oil and test tube, and then to your eye.
  • Why do the objects disappear?

Because they have the same _________________________�(bend light the same way)

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158C: Who studied this concept?

  • Pierre de Fermat:
    • Fields of study were math and law
    • Alive from 1607-1665
    • Fermat’s Principle: light travels the path of “least time”
  • Example: evaluate the quickest path between the dots A & B

A

B

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158C Continued �How does Fermat’s Principle apply here?

Emily (E) looks into the swamp and sees her friend Matthew (M) yelling. He is in over his head! She knows she has to get to Matthew as fast as possible. Which route should she take?

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158D: Thomas Young’s Double Slit Diffraction Experiment

Flipppping Phyyyyysics :)

What follows is prep for the laser lab (via a demo) we’re doing Friday.

Learning at Home (HW) Video: Introduction to Thomas Young's 1801 Double Slit Experiment: Video

Learning at Home (HW) Video Questions:

  1. What does it mean for light to be monochromatic?
  2. Are the areas of constructive interference red, or dark?
  3. If, instead of seeing the pattern of light and dark, we just saw two dots, what would that mean?

Curious about Refraction, or how Mirages work? This is not HW, but if you’re curious…

  1. Introduction to the Refraction of Light and The Index of Refraction: Video
  2. Understanding how a Mirage Works - Refraction of Light: Video

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