● The back side ● Where virtual images are formed
Diagram for Signs
Sign Conventions for Mirrors
Ray Diagrams ● A ray diagram can be used to determine the position and size of an image. ● They are graphical constructions which tell the overall nature of the image. ● They can also be used to check the parameters calculated from the mirror and magnification equations.
Drawing A Ray Diagram ● To make the ray diagram, you need to know ● The position of the object ● The position of the center of curvature ● Three rays are drawn ● They all start from the same position on the object ● The intersection of any two of the rays at a point locates the image. ● The third ray serves as a check of the construction.
The Rays in a Ray Diagram ● Ray 1 is drawn parallel to the principle axis and is reflected back through the focal point, F. ● Ray 2 is drawn through the focal point and is reflected parallel to the principle axis. ● Ray 3 is drawn through the center of curvature and is reflected back on itself.
Notes About the Rays ● The rays actually go in all directions from the object. ● The three rays were chosen for their ease of construction. ● The image point obtained by the ray diagram must agree with the value of q calculated from the mirror equation.
Ray Diagram Examples ● Note the changes in the image as the object moves through the focal point.
Ray Diagram for Concave Mirror, p > R ● The object is outside the center of curvature of the mirror. ● The image is real. ● The image is inverted. ● The image is smaller than the object.
Ray Diagram for a Concave Mirror, p < f ● The object is between the mirror and the focal point. ● The image is virtual. ● The image is upright. ● The image is larger than the object.
Ray Diagram for a Convex Mirror ● The object is in front of a convex mirror. ● The image is virtual. ● The image is upright. ● The image is smaller than the object.
Notes on Images ● With a concave mirror, the image may be either real or virtual. ● When the object is outside the focal point, the image is real. ● When the object is at the focal point, the image is infinitely far away. ● When the object is between the mirror and the focal point, the image is virtual. ● With a convex mirror, the image is always virtual and upright. ● As the object distance increases, the virtual image gets smaller.
Images Formed by Refraction ● Rays originate from the object point, O, and pass through the image point, I ● When n 2 > n 1 , ● Real images are formed on the side opposite from the object.
Sign Conventions for Refracting Surfaces
Flat Refracting Surface ● The image formed by a flat refracting surface is on the same side of the surface as the object. ● The image is virtual.
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- Spring '08
- Light, Geometrical optics, rays