Demos: 7A-05 Candle Illusion

A candle, hidden from direct view, is placed in front of a plane sheet of glass. A beaker containing an identical, unlit, candle is placed behind the glass at a position which causes the reflection of the front candle to be superimposed. To the class, it appears that the candle in the beaker is burning. Then a liquid is poured into the beaker, filling it past the candle flame image.

Directions: Dim the room lights. Stand between the front candle and the class, preventing them from seeing the candle and its shield. Light the candle. If you have not positioned the beaker ahead of time, do it before moving away. Then show the class that the candle is “burning” in the beaker. Then pick up the beer bottle and slowly pour the liquid into the beaker.

Suggestions for Presentation: Because of the nature of reflection, students in all parts of the room will see that the candle flame is directly on the wick of the rear candle, giving the illusion that it is burning. After pouring the liquid in the beaker, you might pick up the beaker and show it to the class. The class will notice that the candle is still in the same place, now seeing the reflection in its entirety.

You can also have a student measure the distance of the front candle from the glass and also the distance of the rear candle from the glass. These will be found to be the same.

Applications: Virtual images in plane mirrors

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