Comparison of Images Formed by Plane, Cylindrical (concave side), and
Spherical (concave side) Mirrors

Springer, Ellen                          Nazareth Academy
1209 W. Ogden Ave.                       354-0061
La Grange Park, IL 60525
352-1886

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 recognize that one's eyes lie along a horizontal axis, and one's 
  forehead and chin lie along a vertical axis.

4) To help students recognize that right to left and top to bottom 
  reversals occur simultaneously, and occur only in curved mirrors.

5) 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, or as 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.