Chapter 11.pdf

Drawing a Concave Mirror Ray DiagramWhen you draw ray diagrams, you can sketch in the object or use anupright arrow to represent the object, as shown in Figure 11.12. Showreal rays as solid lines. Use dashed lines to present virtual rays, whichare rays that only appear to exist behind the mirror. Follow the steps inFigure 11.12 to draw a ray diagram of a concave mirror.ray 1ray 2FobjectimageFigure 11.12 Concave mirror ray diagram1. The first ray of a concave mirror ray diagramtravels from a point on the object parallel to theprincipal axis (ray 1). Any ray that is parallel tothe principal axis will reflect through the focalpoint on a converging mirror.2. The second ray travels from a point on theobject toward the focal point (ray 2). Any raythat passes through the focal point on aconverging mirror will be reflected back parallelto the principal axis.3. Draw the real image where the rays intersect.Some Uses for Concave MirrorsConcave mirrors are specially designed to collect light and bring it to asingle point. This is why concave mirrors are used in telescopes tocollect light rays from a great distance and bring them together.Can concave mirrors be used to send out beams of light rays as well?Imagine that a bright light were placed at the focal point of a concavemirror and allowed to shine into the mirror in Figure 11.10 on theprevious page. By reversing the direction of the arrows in the ray diagram,you can see that the light rays would leave the mirror as parallel rays.That is why you will find concave mirrors in flashlights, car headlights,dental examination lights, and other applications (Table 11.2).Table 11.2 Some Uses of Concave MirrorsDeviceFlashlightUse of Concave MirrorTo produce a parallel beamTelescopeTo collect light from a distant source andfocus it for viewingFigure 11.13 The concave mirror forthe Hubble telescope is beingprepared for launch into space.Cosmetic mirrorHeadlightsof a carTo produce an enlarged imageTo produce a parallel beam of light that canbe directed down (low beam) or straightahead (high beam)422UNIT DLight and Geometric Optics