RefractionChapter 15

Refraction

• Refraction: The bending of light as it travels from one medium to another

• Refraction occurs when light’s velocity changes

• The speed of light varies with the medium

Refraction

Θr = Angle of Refraction

Θi = Angle of Incidence

Index of Refraction

• Index of Refraction = speed of light in vacuum

speed of light in medium

medium in thelight of speed

vaccuumain light of speed

v

cn

*Only valid for light with wavelength of 589 nm in a vacuum (p. 564)

Snell’s Law

Snell’s Law determines the angle of refraction

nisin(θi) = nrsin(θr)

ni = Index of refraction of first medium

nr = Index of refraction of second medium

θi = Angle of Incidence

θr = Angle of Refraction

Bending relative to the normal

• When light passes from a medium with a low index of refraction to a medium with a high index of refraction, the ray bends toward the normal

• When light passes from a medium with a high index of refraction to a medium with a low index of refraction, the ray bends away from the normal

CATBEAR trying to catch a fish!!!

Sample Problem (p.567 #4)

• Sunlight passes into a raindrop at an angle of 22.5° from the normal at one point on the droplet. What is the angle of refraction?

Sunlight into a raindrop

• Will the ray bend away from the normal or towards the normal?– Low n to high n, the ray will bend toward the

normalθi

θr

Use Snell’s Law

rrii nn sinsin

r

iir n

n

sinsin

68.16333.1

)5.22)(sin(1(sin

sinsin 11

r

iir n

n

The Catbear lyrics

When catbear was just a kittenHis mom was killed by a kid wearing mittensThe little cat searched far and wideFor a friend to be by his side

One day a hunter captured a bear cubWhile its mom was out hunting for grubWhen the bear returned to her denA kitten was where her cub had been

Chorus: Catbear, The CatbearHe looks like a cat, he thinks like a bearCat bear, The CatbearHe’s Trying to catch a fish that’s really not there

Catbear (lyrics continued) The bear raised the kitten as her son

 They had each other, so both of them won

 The kitten had only one wish

 To learn to catch a really big fish

 

So one day they went to a pier

The bear told him he had nothing to fear

Snell’s Law will guide your claws

And soon that fish will be in your paws

Well along came a poor fish

 Who didn’t know he’d be a tasty dish

 The kitten used the laws of refraction

  And the wooden boards to get good traction

He caught the fish with one big swipe

  And gulped it down without a gripe

    The fish cried “It’s not fair!”

    Due to refraction, the cat’s in the air!

Chorus: Catbear, The Catbear, he looks like a cat, but thinks like a bear!

 Catbear, The Catbear, he’s trying to catch a fish that’s really not there!

Well the bear was proud of her offspring

            And thought of all the fish he would bring

            She said they were quite the pair

            And named her son…THE CATBEAR!!

          Chorus (repeat 3x)

Real life best friends

http://www.dailymail.co.uk/news/article-1026216/Pictured-The-cat-bear-best-friends-simply-bear-apart.html