1. Refraction 15-1

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

3. Refraction Why does the lawnmower turn when it strikes the grass? The right wheel slows down before the left one. Light waves behave in the same way. Refraction is the bending (change in direction) of light when it travels from one medium into another. Caused by a change in speed

4. How does it bend? Wave fronts (dashed lines) slow down when entering glass. Wave fronts (dashed lines) slow down when entering glass. The lower edge slows before the upper edge, so the wave turns to the right. The lower edge slows before the upper edge, so the wave turns to the right. Also, the wavelength is shortened. Also, the wavelength is shortened. Lower edge Upper edge

5. Click below to watch the Visual Concept. Visual Concept Wave Model of Refraction

6. Ray Diagrams Light rays reflect and refract. If the light slows down, it bends toward the normal line (  glass <  air ). Angles are measured with the normal line. Light rays are reversible.

7. Law of Refraction Light passing from one material to another is refracted (bent) by a fractional angle that depends on the optical properties of each material.

8. Law of Refraction c = 3  10 8 m/s v is always less than c, so n >1 for all media. n air = 1.000293 n is the index of refraction (depends on the material) n is dimensionless.

9. Indices of Refraction

10. Snell’s Law Angles must be measured with the normal.

11. Classroom Practice Problems Find the angle of refraction of a light ray (589 nm) entering diamond (n=2.419) from water (n=1.333) at an angle of 30.00° with the normal. Find the angle of refraction of a light ray (589 nm) entering diamond (n=2.419) from water (n=1.333) at an angle of 30.00° with the normal. Answer: 15.99° Answer: 15.99° A light ray (589 nm) traveling through air strikes an unknown substance at 60.00° and forms an angle of 41.42° with the normal inside. What material is it? A light ray (589 nm) traveling through air strikes an unknown substance at 60.00° and forms an angle of 41.42° with the normal inside. What material is it? Answer: n = 1.309, so the material is ice Answer: n = 1.309, so the material is ice

12. Refraction Where does the cat see the fish? Where does the fish see the cat? Objects appear to be in line with the observed rays. Light rays bend (refract) passing from water to air, making objects appear to be shallower and closer to the observer.

13. Now what do you think? Suppose you are reaching for swim goggles floating below the surface of a pool. Would you reach at the point where you see the object, or above it, or below it? Suppose you are reaching for swim goggles floating below the surface of a pool. Would you reach at the point where you see the object, or above it, or below it? If you are under water looking at a person standing on the side of the pool, where is the image? If you are under water looking at a person standing on the side of the pool, where is the image?