Figure 4 Convex mirrors can only form virtual images. A When parallel incoming rays strike a convex mirror, they are reflected away from one another. B Convex mirrors always form virtual images that are upright and smaller than the object. Because of their reduced image size, convex mirrors on automobiles warn that “Objects are closer than they appear.”
ddConvex Mirrors
When the outside surface of a curved mirror is the reflecting surface, the mirror is a convex mirror. Figure 4A shows how a convex mirror reflects parallel light rays. Note how the curvature of the convex mirror causes the reflected rays to spread out.
Convex mirrors always cause light rays to spread out and can only form virtual images. Figure 4B shows how a convex mirror forms a virtual image. As the rays from the object reflect from the mirror, the rays spread out. Because they appear to be coming from a point behind the mirror, that is where the image appears. The image formed by a convex mirror is always upright and smaller than the object. This allows the mirror to show a wide angle of view. Because of their wide angle of view, round, convex mirrors are often used in store aisles, at hazardous traffic intersections, and for side mirrors on automobiles.
Section 19.1 Assessment
Reviewing Concepts
- How is the angle of incidence of a light ray related to the angle of reflection?
- What type of image does a plane mirror form?
- What types of image can be produced by a concave mirror? A convex mirror?
How are real images different from virtual images?
Why can convex mirrors form only one type of image?
Critical Thinking
Applying Concepts Explain why a plane mirror cannot form a real image.
Inferring If you place an object 10 cm from a particular concave mirror, a virtual image forms behind the mirror. What can you infer about the focal point of the mirror?
Applying Concepts If you look inside the bowl of a shiny metal spoon, your image is upside down. If you look at the outside of the bowl, your image is right side up. Explain.
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