Description:

This exhibit consists of a sheet of plexi-glass and two floodlights controlled by dimmer switches. Users sit on opposite sides of the plexiglass and adjust the light intensity until they merge their reflection with the image of their partner's face.

Purpose:

This apparatus demonstrates the Law of Reflection that states that a reflected image will always appear as far behind the reflecting surface as the object is in front of the reflecting surface.

Classroom Instructions:

1. Set apparatus on a table and plug it in. Lights on apparatus may have to be adjusted so they shine on the students who will be sitting on each side.

2. Have two students sit, one on each side of apparatus, approximately the same distance away from the apparatus.

3. Students need to line up their eyes and nose as best as they can.

4. Have students manipulate the lights so that one is bright while the other is dim. (Have the class observe from the bright side. Remind the student sitting on the dim side that they will not see what everyone's laughing at.)

5. Have students switch the lighting so the student on the dim side during the first try will get a chance to see why everyone is laughing.

Hints:

Prepare students for this exhibit by asking questions such as:

• How would you look with long or short hair? glasses? a beard? ...
• What happens to the reflection of objects as light passes through a clear pane?
• Does the distance from the pane effect the reflection?

Make sure apparatus in on a sturdy surface while in use.

Check cords periodically for frayed ends.

Extensions:

Teachers may want to set up the traditional candle Exploration reflection as another demonstration of the Law of Reflection.

Another variation to the reflection pattern is to set up a tic-tac-toe game on either side of the plexi-glass and try to play the game by using the reflections to determine where to place your pieces. (Check with your math teachers to see if they have any "mira" mirrors. These work well for this last game.)

References:

1. Schaefer, D., "Science Experiments on File - Images Formed by Plane Mirrors", Facts on File, Inc. 460 park Ave. S., New York, NY. 10016 Pgs. 233-235.

2. Delta Science Module - "Lenses & Mirrors", Delta Education, P.O. Box 915, Hudson, N.H. 03051

3. "Science Snackbook", Exploratorium, San Francisco, CA.

4. "Exploratorium Cookbook III, recipe # 171, Exploratorium, San Francisco, CA.

Exhibit CONSTRUCTION DIRECTIONS

"Ready to Use" EXHIBIT SIGN

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