17.2 Mirrors, Lenses, and Images

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. 2

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

Inv 17.2 Mirrors, Lenses, and Images Investigation Key Question: How does a lens or mirror form an image? 4

17.2 Mirrors, Lenses, and Images We see a world of images 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 most 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 converging 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.

A converging lens bends an incident light ray parallel to the optical axis toward the focal point. A diverging lens bends an incident light ray parallel to the axis outward, away from the focal point 9

17.2 The image formed by a lens A lens can form a virtual image just as a 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 diagrams 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 parallel 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).

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17.2 Characteristics of images A real image is formed by the actual intersection of light rays from the object. Real images can be projected on a surface.

17.2 Characteristics of images A converging lens acts as a magnifying glass when the object is closer to the lens than one focal length.

17.2 Characteristics of images A diverging lens is thicker around the edges and thinner in the center. The image formed by a diverging lens is virtual and right side up.

17.2 Characteristics of images The magnification varies for single lenses- it depends on the distance of the object from the lens.