Refraction 15-1. What do you think? Suppose you are reaching for swim goggles floating below the surface of a pool or trying to net a fish while out in.

RefractionRefraction

15-115-1

What do you think?What do you think?

Suppose you are reaching for swim Suppose you are reaching for swim goggles floating below the surface of goggles floating below the surface of a pool or trying to net a fish while a pool or trying to net a fish while out in a lake. Would you reach at the out in a lake. Would you reach at the point where you see the object, or point where you see the object, or above it, or below it? above it, or below it?

RefractionRefraction

Why does the lawnmower turn when it strikes the Why does the lawnmower turn when it strikes the grass?grass? The right wheel slows down before the left one.The right wheel slows down before the left one. Light waves behave in the same way.Light waves behave in the same way.

RefractionRefraction is the bending (change in direction) of is the bending (change in direction) of light when it travels from one medium into another.light when it travels from one medium into another. Caused by a change in speedCaused by a change in speed

How does it bend?How does it bend?

Wave fronts (dashed lines) slow down when Wave fronts (dashed lines) slow down when entering glass.entering glass. The lower edge slows before the upper edge, so The lower edge slows before the upper edge, so

the wave turns to the right.the wave turns to the right. Also, the wavelength is shortened.Also, the wavelength is shortened.

Lower

edge

Upper

edge

Click below to watch the Visual Concept.

Visual Concept

Wave Model of Wave Model of RefractionRefraction

Ray DiagramsRay Diagrams

Light rays reflect and refract.Light rays reflect and refract. If the light slows down, it bends toward the normal line If the light slows down, it bends toward the normal line

((glassglass < < airair).). Angles are measured with the normal line.Angles are measured with the normal line.

Light rays are reversible.Light rays are reversible.

Law of RefractionLaw of RefractionLight passing from Light passing from

one material to one material to another is another is refracted (bent) refracted (bent) by a fractional by a fractional angle that angle that depends on the depends on the optical properties optical properties of each material.of each material.

Law of RefractionLaw of Refraction

cc = 3 = 3 10 1088 m/s m/s vv is always less than is always less than c,c, so so nn >1 for all media. >1 for all media.

nnairair = 1.000293 = 1.000293 n n is the index of refraction (depends on the material)is the index of refraction (depends on the material) nn is dimensionless. is dimensionless.

Indices of RefractionIndices of Refraction

Snell’s LawSnell’s Law

Angles Angles mustmust be measured be measured with the with the normal.normal.

Classroom Practice Classroom Practice ProblemsProblems

Find the angle of refraction of a light ray Find the angle of refraction of a light ray (589 nm) entering diamond (n=2.419) (589 nm) entering diamond (n=2.419) from water (n=1.333) at an angle of from water (n=1.333) at an angle of 30.00° with the normal.30.00° with the normal. Answer: 15.99°Answer: 15.99°

A light ray (589 nm) traveling through air A light ray (589 nm) traveling through air strikes an unknown substance at 60.00° strikes an unknown substance at 60.00° and forms an angle of 41.42° with the and forms an angle of 41.42° with the normal inside. What material is it?normal inside. What material is it? Answer: Answer: nn = 1.309, so the material is ice = 1.309, so the material is ice

RefractionRefraction

Where does the cat see the fish?Where does the cat see the fish? Where does the fish see the cat?Where does the fish see the cat? Objects appear to be in line with the observed rays.Objects appear to be in line with the observed rays.

Light rays bend (refract) passing from water to air, making Light rays bend (refract) passing from water to air, making objects appear to be shallower and closer to the observer.objects appear to be shallower and closer to the observer.

NowNow what do you what do you think?think?

Suppose you are reaching for swim Suppose you are reaching for swim goggles floating below the surface of goggles floating below the surface of a pool. Would you reach at the point a pool. Would you reach at the point where you see the object, or above where you see the object, or above it, or below it? it, or below it?

If you are under water looking at a If you are under water looking at a person standing on the side of the person standing on the side of the pool, where is the image?pool, where is the image?