PURPOSE: To demonstrate the Leidenfrost effect.
DESCRIPTION: Turn on the hot plate to high for about two minutes to pre-heat the aluminum sheet/skillet. Then squirt a few large drops of water (with green food coloring to make it visible) onto the aluminum skillet. The water forms drops which skitter around on the hot plate for an unexpectedly long duration, because of an insulating layer of water vapor (steam). Big drops can be created which will persist for a minute or longer, while executing interesting oscillations. This is known as the Leidenfrost phenomenon.
SUGGESTIONS:
Click here to view a discussion of dangerous Leidenfrost demonstration experiments, written by Professor Jearl Walker for one of the Halliday and Resnick textbooks. (A copy of this article is in the Demonstration Reference File.)Click here to read about an attempt gone awry at putting liquid nitrogen in your mouth to create a vaporous plume.
REFERENCES: (PIRA 4B50.30) See also videotape "Leidenfrost Phenomena" by Prof. Jearl Walker, in our collection.
EQUIPMENT: Aluminum sheet on hot plate with squeeze jar of green water.
SETUP TIME: None.
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