Refraction

1
Refraction

• when light passes from one material (aka medium)
  to another, it bends because the speed of light
  travels at different speeds in different mediums

2
Light bends toward the normal when it slows
down, and away from the normal as it speeds up.
- vacuum 3.0 x 108 m/s - water 2.26 x 108
m/s - acrylic 1.76 x 108 m/s
3
Light travels thru water

• (why we see blue best)

4

• This bending of light can play tricks on our
  minds. Ie. Broken/Bend pencil/spoon.

5

• This is why a fish in the water looks just below
  the surface, and may be deeper and further away.

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Another Trick
Light travels faster at higher altitudes because
the air is less dense.
7

• Another example of refraction of light is the
  twinkling of a star in the night sky
• As starlight travels from space into the Earths
  atmosphere, the rays are refracted.
• Since the atmosphere is constantly changing, the
  amount of refraction also changes.

8

• Light can undergo partial reflection and
  refraction at the same time at a surface.
• Ex. Sunglasses, two way mirrors (buildings less
  air conditioning)

9
Refraction Lab
Purpose To determine relative speeds of light
through different mediums

• Observations
• 1. Trace a petri dish, label the normal and draw
  in an incident light ray for you to follow.
• 2. Fill the petri dish with water
• 3. Shoot the light ray down the incident ray.
• 4. Trace the light ray coming out of the petri
  dish
• 5. Remove petri dish and connect the lines and
  label water
• 6. Repeat steps 2 5 with glycerin in petri
  dish.
• 7. Use a protractor to label the incident angle
  and both of the refracted angles.

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• Analysis
• Which ray bends most toward the normal air,
  water, glycerin? Which ray bends the least?
• Which substance is the light travelling the
  fastest in and why?
• Which substance is the light travelling the
  slowest in and why?

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• Dispersion
• - The refraction of white light into different
  colours. (Pink Floyd dark side of the moon)
• - Since each colour travels at a different
  speeds, it bends at different angles

12

• Ex. Rainbows in order to see a complete
  rainbow, you need to stand so that its raining in
  front of you, and the sun is directly behind you.

13
Total Internal Reflection

• Sometimes light bends (refracts) so much that
• it hits the inside wall of a substance at 90
  degrees,
• and totally reflects off (no refraction occurs).
  The light gets trapped inside the
• object.

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Ex. Fiber Optics used to send signals quickly
over long distances glasses, phone cables,
surgery
Demo dollar store fibre optics
Demo laser follows stream of water (2L water
bottle)
15

• Ex. Diamonds
• jewellers cut angles surfaces (facets) to
  make the light become trapped in diamond, and
  reflect out the top, making it sparkle.

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Prisms
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• Pg. 503 1 3, 7