Refraction Chapter 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 Θ r = Angle of Refraction Θ i = Angle of Incidence

Index of Refraction Index of Refraction = speed of light in vacuum speed of light in medium

*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 n i sin(θ i ) = n r sin(θ r ) n i = Index of refraction of first medium n r = Index of refraction of second medium θ i = Angle of Incidence θ r = 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 normal θiθi θrθr

Use Snell’s Law

The Catbear lyrics When catbear was just a kitten His mom was killed by a kid wearing mittens The little cat searched far and wide For a friend to be by his side One day a hunter captured a bear cub While its mom was out hunting for grub When the bear returned to her den A kitten was where her cub had been Chorus: Catbear, The Catbear He looks like a cat, he thinks like a bear Cat bear, The Catbear He’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