17.1 Reflection and Refraction

1. 17.1 Reflection and Refraction

2. Chapter 17 Objectives Describe the functions of convex and concave lenses, a prism, and a flat mirror. Describe how light rays form an image. Calculate the angles of reflection and refraction for a single light ray. Draw the ray diagram for a lens and a mirror showing the object and image. Explain how a fiber-optic circuit acts like a pipe for light. Describe the difference between a real image and a virtual image and give an example of each.

3. Chapter 17 Vocabulary Terms • angle of refraction • chromatic • aberration • converging lens • critical angle • diffuse reflection • dispersion • diverging lens • eyepiece • fiber optics • focal length • focal plane • focal point • focus • geometric optics • image • image relay • incident ray • index of refraction • law of reflection • lens • magnification • magnifying glass • mirror • normal line • object • objective • optical axis • optics • prism • ray diagram • real image • reflected ray • refracting telescope • Snell’s law • specular reflection • spherical aberration • telescope • thin lens formula • total • internal reflection • virtual

4. Inv 17.1 Reflection and Refraction Investigation Key Question: How do we describe the reflection and refraction of light?

5. 17.1 Reflection and Refraction The overall study of how light behaves is calledoptics. • The branch of optics that focuses on the creation of images is called geometric optics, because it is based on relationships between angles and lines that describe light rays.

6. 17.1 Reflection and Refraction A lens is an optical device that is used to bend light in a specific way. A converging lens bends light so that the light rays come together to a point. A diverging lens bends light so it spreads light apart instead of coming together.

7. 17.1 Reflection and Refraction Mirrors reflect light and allow us to see ourselves. A prism is another optical device that can cause light to change directions. A prism is a solid piece of glass with flat polished surfaces.

8. 17.1 Reflection Images appear in mirrors because of how light is reflected by mirrors. Theincident ray follows the light falling onto the mirror. The reflected ray follows the light bouncing off the mirror.

9. 17.1 Reflection In specular reflection each incident ray bounces off in a single direction. A surface that is not shiny creates diffuse reflection. In diffuse reflection, a single ray of light scatters into many directions.

10. Law of Reflection The incident ray strikes the mirror. The reflected ray bounces off. The angle of incidence equals the angle of reflection.

11. Law of reflection A light ray is incident on a plane mirror with a 30 degree angle of incidence. Sketch the incident and reflected rays and determine the angle of reflection. • You are given the angle of incidence. • Use the law of reflection which states the angle of reflection equals the angle of incidence. • Sketch a ray diagram showing the angle of reflection is 30o. • You are asked for a ray diagram and the angle of reflection.

12. 17.1 Refraction Light rays may bend as they cross a boundary from one material to another, like from air to water. This bending of light rays is known as refraction. The light rays from the straw are refracted (or bent) when they cross from water back into air before reaching your eyes.

13. 17.1 Refraction When a ray of light crosses from one material to another, the amount it bends depends on the difference in index of refraction between the two materials.

14. 17.1 Index of refraction The ability of a material to bend rays of light is described by the index of refraction (n).

15. 17.1 Snell's law of refraction Snell’s law is the relationship between the angles of incidence and refraction and the index of refraction of both materials. Angle of refraction (degrees) Angle of incidence (degrees) ni sini= nr sin r Index of refraction of incident material Index of refraction of refractive material

16. 17.1 Relection and the critical angle • The angle of incidence at which light begins reflecting back into a refractive material is called the critical angle. • The critical angle depends on the index of refraction.

17. Calculating the angle of refraction • You are asked for the angle of refraction. • You are given the angle of incidence, and materials. • Use Snell’s law: ni sin i = nr sin r • Solve sin r = 1.00 sin (30o) ÷ 1.33 sin r = 0.376 r = sin-1 (0.376) = 22o A ray of light traveling through air is incident on a smooth surface of water at an angle of 30° to the normal. Calculate the angle of refraction for the ray as it enters the water.

18. 17.1 Dispersion and prisms When white light passes through a glass prism, blue is bent more than red. Colors between blue and red are bent proportional to their position in the spectrum.

19. 17.1 Dispersion and prisms The variation in refractive index with color is called dispersion. A rainbow is an example of dispersion in nature. Tiny rain droplets act as prisms separating the colors in the white light rays from the sun.