Comparison of Images Formed by Plane, Cylindrical and Spherical Mirrors 






Jim Szeszol                        Naperville Central High School
29 Mayfair Lane                    440 W. Aurora
Aurora IL 60504                    Naperville IL 60540
(708) 898-6603                     (708) 420-6417
                                   
Objectives:

1) To demonstrate that all mirrors reverse the image front to back and that the 
   apparent right to left reversal in a plane mirror is a result of this front 
   to back reversal. 
2) To describe plane, cylindrical and concave mirrors in terms of curvature 
   about horizontal and vertical axes. 
3) To help students recognize that right to left and top to bottom reversals 
   occur simultaneously and occur only in curved mirrors. 
4) To discover that left to right reversals (and top to bottom reversal) occur 
   when the axis of the object is parallel to the curved axis of the mirror and 
   that no left to right reversal occurs when the axis of the object is along a 
   linear mirror axis. 

Apparatus Needed:

Plane mirror, cylindrical mirror, concave mirror of short focal length.  The 
cylindrical mirror can be made by gluing a piece of aluminized mylar inside a 
120o section of carpet roll. 

Recommended Strategy:

1) This exercise can be done anytime during the year as an attention grabber, 
   an introduction to, or review of mirror images. 
2) In order to avoid confusion which is associated with left and right in 
   observing mirror images, it seems best to describe orientation along a 
   horizontal axis in terms of some objects in the room such as the window side 
   and door side. 
3) Beginning with a plane mirror ask the students to observe the image of their 
   left hand.  Ask if the image is reversed left to right.  Most will reply that 
   it is.  Then ask if the image is reversed to bottom.  Point out the 
   inconsistency of their answer and let them sit with that for a while. 
4) Using a plane mirror ask the student to cover their eye which is on the wall 
   side; ask them which eye is covered in the mirror (wall side or window side.)  
   Also ask if the image is reversed top to bottom.  Direct the students to turn 
   the mirror through 90o, make observations and answer the same questions. 
5) Using the concave side of a cylindrical mirror, repeat No. 4 above, asking 
   the same questions. 
6) Using the concave side of a spherical mirror, repeat No. 4 above, asking the 
   same questions. 
7) Summarize student observations on the board and help the class explain their 
   observations. 
8) Observations in a cylindrical mirror can be extended by viewing the image of 
   two different colored arrows crossed at 90o.  Ask the students to turn the 
   object through 90o and observe what happens to the image.  Ask them to turn 
   the mirror through 90o and observe what happens to the image this time.