Comparison of Images Formed by Plane, Cylindrical (concave side), and
Spherical (concave side) Mirrors
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Springer, Ellen Nazareth Academy
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.
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.
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