1、,了解光学知识,Unit 6: Light and Optics,17.1 Reflection and Refraction17.2 Mirrors, Lenses, and Images17.3 Optical Systems,Chapter 17 Light and Color,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 ang
2、les 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.,Chapter 17 Voca
3、bulary Terms,lens mirror prism optics geometric opticsspecular reflection diffuse converging diverging law of reflectionnormal line ray diagram magnification object,index of refractionfocal point focal length optical axis light ray magnificationcritical angle Snells law real image virtual image chro
4、matic aberrationrefraction fiber optics dispersion,magnifying glass spherical aberrationreflection diffraction telescope focus total internal reflectionresolution pixel image focal plane thin lens formula,17.1 Reflection and Refraction,Key Question:How do we describe the reflection and refraction of
5、 light?,*Students read Section 17.1 AFTER Investigation 17.1,17.1 Reflection and Refraction,The overall study of how light behaves is called optics. 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 t
6、hat describe light rays.,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.,17.1 Refl
7、ection 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.,17.1 Reflection,Images appear in mirrors because of how light is reflected by mirrors.
8、The incident ray follows the light falling onto the mirror. The reflected ray follows the light bouncing off the mirror.,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
9、ray of light scatters into many directions.,Law of Reflection,The angle of incidence equals the angle of reflection.,The incident ray strikes the mirror.The reflected ray bounces off.,17.1 Law of reflection,A light ray is incident on a plane mirror with a 30 degree angle of incidence. Sketch the inc
10、ident and reflected rays and determine the angle of reflection.,30o,30o,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
11、 cross from water back into air before reaching your eyes.,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.,17.1 Index of refraction,The ability of a material to bend rays of ligh
12、t is described by the index of refraction (n).,17.1 Snells law of refraction,Snells law is the relationship between the angles of incidence and refraction and the index of refraction of both materials.,ni sin Qi = nr sin Qr,Index of refraction of refractive material,Angle of incidence (degrees),Angl
13、e of refraction (degrees),Index of refraction of incident material,17.1 Calculate the angle of refraction,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.,17.1 Dispersi
14、on 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.,17.1 Dispersion and prisms,The variation in refractive index with color is called dispersion.A rainbow is an example of dispers
15、ion in nature. Tiny rain droplets act as prisms separating the colors in the white light rays from the sun.,17.2 Mirrors, Lenses, and Images,Key Question:How does a lens or mirror form an image?,*Students read Section 17.2 AFTER Investigation 17.2,17.2 Mirrors, Lenses, and Images,We see a world of i
16、mages created on the retina of the eye by the lens in the front of the eye.,17.2 Mirrors, Lenses, and Images,Objects are real physical things that give off or reflect light rays. Images are “pictures” of objects that are formed in space where light rays meet.,17.2 Mirrors, Lenses, and Images,The mos
17、t common image we see every day is our own reflection in a mirror.The image in a mirror is called a virtual image because the light rays do not actually come together.,The virtual image in a flat mirror is created by the eye and brain.,17.2 Mirrors, Lenses, and Images,Light rays that enter a converg
18、ing lens parallel to its axis bend to meet at a point called the focal point.The distance from the center of the lens to the focal point is called the focal length.The optical axis usually goes through the center of the lens.,17.2 The image formed by a lens,A lens can form a virtual image just as a
19、mirror does.Rays from the same point on an object are bent by the lens so that they appear to come from a much larger object.,17.2 The image formed by a lens,A converging lens can also form a real image. In a real image, light rays from the object actually come back together.,17.2 Drawing ray diagra
20、ms,A ray diagram is the best way to understand what type of image is formed by a lens, and whether the image is magnified or inverted.These three rays follow the rules for how light rays are bent by the lens:A light ray passing through the center of the lens is not deflected at all (A).A light ray p
21、arallel to the axis passes through the far focal point (B).A light ray passing through the near focal point emerges parallel to the axis (C).,17.3 Optical Systems,Key Question:How are the properties of images determine?,*Students read Section 17.3 AFTER Investigation 17.3,An optical system is a coll
22、ection of mirrors, lenses, prisms, or other optical elements that performs a useful function with light.Characteristics of optical systems are:The location, type, and magnification of the image.The amount of light that is collected.The accuracy of the image in terms of sharpness, color, and distorti
23、on.The ability to change the image, like a telephoto lens on a camera.The ability to record the image on film or electronically.,17.3 Optical Systems,17.3 The sharpness of an image,Defects in the image are called aberrations and can come from several sources.,Chromatic aberration is caused by disper
24、sion, when different colors focus at different distances from the lens.,17.3 The sharpness of an image,Spherical aberration causes a blurry image because light rays farther from the axis focus to a different point than rays near the axis.,17.3 The sharpness of an image,Diffraction causes a point on
25、an object to focus as a series of concentric rings around a bright spot.,17.3 Thin lens formula,The thin lens formula is a mathematical way to do ray diagrams with algebra instead of drawing lines on graph paper.,1 + 1 = 1do didf,focallength (cm),Image distance(cm),Objectdistance(cm),17.3 Use the thin lens formula,Calculate the location of the image if the object is 6 cm in front of a converging lens with a focal length of 4 cm.,17.3 Image relay,A technique known as image relay is used to analyze an optical system made of two or more lenses.,Application: The Telescope,
