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Home Minds On Reflection and Mirrors Mission RM8 Convex Mirror Ray Tracing Help Help 7

Mission RM8 Convex Mirror Ray Tracing

The Question

The following diagrams are ray diagrams, showing how to locate the image (in GREEN) of an 'arrow object' (in RED). Which of these diagrams are correctly drawn and show the proper image location, size and orientation?

Physics Rules

Drawing Ray Diagrams:
Ray diagrams involve the construction of two or more rays from a location on the object in order to determine the location of the image. The principle is that the image is at the location where all the reflected light seems to come from. By drawing two or more incident rays and their corresponding reflected rays, the image location can be identified as the intersection point of the reflected rays. So a point on the extremity of the object is selected (the arrowhead in these diagrams). Then two of the three rules of reflection are used to draw two sets of incident and reflected rays (see Know the Law section below). The location where the reflected rays intersect is the image location of the top of the arrowhead. The remainder of the image extends from the principal axis to the image of the arrowhead.

Game Plan

You are to identify the diagrams that are correctly drawn. The Know the Law section describes the method used to draw ray diagrams. Check each diagram carefully, making sure that the ...
  • ... principal rays were drawn starting from the arrowhead of the object
  • ... principal rays were drawn correctly (see Know the Law below)
  • ... image was located where the principal rays intersected
  • ... image exhibits the proper characteristics - virtual, reduced in size, upright and located between the focal point and the mirror.
If the diagram fails at any of the above four criteria, then you can instantly conclude that the diagram is not correct.

Physics Rules

Convex Mirrors - Rules of Reflection
Light reflects off any surface - plane mirror, curved mirror, or non-mirror - according to the law of reflection. For convex mirrors, some generalizations can be made to simplify ray construction. They are:
  • An incident ray traveling parallel to the principal axis will reflect and travel in line with the focal point.
  • An incident ray traveling towards the focal point (on the opposite side of the mirror) will reflect and travel parallel to the principal axis.
  • An incident ray traveling towards the center of curvature (on the opposite side of the mirror) will reflect and travel back along the same path from which it came.

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