DO NOW: EM
journals in In Box.
Then…Using
appropriate vocab
terms, please
explain exactly what
is going on in this
photo. Does light
change media?
Speed up? slow
down? Bend?
Refract? BE
COMPLETE!
Q & A Walk
• Participate in the Walk or 5k and get +3 on your
final exam
• Bring me your race bib next week and/or
registration bag to claim your points.
• For info email: rua@robbinsville.k12.nj.us
• Entry fee: $20 before June 8 ($18 for USATF
Members and students 14 and under), $25 on
race day, $18 fitness walk
• Give Ms. Rua your registration form and fee.
• Make Checks Payable to: Robbinsville High
School
• Information on the RHS website
Speed of light…
•
•
•
•
•
Is ‘c’ in a vacuum
Is slower in air
Slower still in water
And even slower in glass
Looking at this picture, you have A LOT of
changing media, and therefore changing
speeds.
• As light slows down, it ‘bends’ (refraction)

Refraction occurs when the average speed of light changes in going from
one transparent medium to another.
o We can understand this by considering the action of a pair of toy
cartwheels connected to an axle as the wheels roll gently downhill from a
smooth sidewalk onto a grass lawn.
o If the wheels meet the grass at some angle, they will be deflected from
their straight-line course. The direction of the rolling wheels is shown by
the dashed line.
o Note that on meeting the lawn, where the wheels roll more slowly owing to
interaction with the grass, the left wheel (YOUR left) slows down first. This
is because it meets the grass while the right wheel (YOUR right) is still on
the smooth sidewalk.
o The faster-moving right wheel tends to pivot about the slower-moving left
wheel because during the same time interval, the right wheel travels
farther than the left one.
• Light from is refracted through the sides of the thick glass
- making the glass appear thinner than it is. The eye is
used to seeing in straight lines, and perceives the root
beer to be at the outer edge of the glass
That frosty mug full of A&W root beer seems to empty so quickly.
What seems like a lot of root beer is actually a lot of glass. The
deception is uncovered when the root beer mug is submerged in
water. When looking at the mug above the water level, there
appears to be a lot of root beer. But when looking at the mug
below the water level, one observes the truth; the water
surrounding the glass minimizes the effect of refraction and
reveals the large quantity of glass. We've been deceived!
Can you think of other products that may use this ‘physics’
illusion to make you think you are getting more product than you
actually are?
• From yesterday’s exit:
(light slows down at
water – it ‘bends’ and
the image appears to
be closer… this
explains quarter, too!)
• Make correction/
additions
changes… questions?
• To explain prism, you must understand that high
frequency light (violet) travels more slowly
through glass than low frequency light (red)
Today’s Demos
• Same as last class:
Demo
Name
Big
Mirrors
Light
Tube
Mirage
What did you SEE Do Now –
Exit – what
happening
why do you ACTUALLY
(words/picture) THINK it was happened?
happening
Luminous vs. Illuminated
• What’s the difference? DISCUSS
• Conclusions?
• Luminous: emits its own light, light source,
shines, etc.
– Examples?
• Illuminated: lit up because other light is
shining on it, does not emit its own light, does
not shine on its own, etc.
– Examples?
So…is Rihanna a physics genius?
• Does ‘shine bright like a
diamond’ make
‘physics’ sense?
DISCUSS
• Thoughts?
So why are diamonds so sparkly?
(Or any reflective surface!)
• Critical angle - the angle of incidence above
which total internal reflection occurs (in other
words, at an angle LARGER THAN the critical
angle, you observe total internal reflection –
TIR)
• TIR only takes place when both of the following
two conditions are met:
– a light ray is in the more dense medium and
approaching the less dense medium.
– the angle of incidence for the light ray is greater
than the critical angle (as mentioned above)
• You can observe
total internal
reflection when
swimming:
• Or with ‘fiber
optics’
• You can observe
total internal
reflection when
swimming:
• Or with ‘fiber
optics’
• Or with
diamonds
Goals
1. See teacher to check in on any previous POGILS
(they should be done and checked by the end of
class)
2. Finish your FINAL POGIL of the school year!
3. Prep for your quest next class!
4. Fill out exit slip and turn in
NEXT CLASS – You will take your quest
NEXT WEEK – you will get your quest back and have
all of next week’s physics classes to prep for finals
(study, work on cheat sheet, complete study
guide  this will be posted on my website this
week for you to print)