Comparison of Images Formed by Plane, Cylindrical and Spherical Mirrors

Jim Szeszol Naperville Central High School
440 W. Aurora
Naperville IL 60540
(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
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.