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One way to cook eggs is to boil them, but once the water has reached boiling point, does it matter if the heat is turned down? With two eggs cooking, the heat is reduced on one, while the other is left at full. To make it a fair test, the eggs are heated for the same amount of time and are taken out of the water at the same time. Despite one egg being cooked in rapidly boiling water and the other not, the eggs cook exactly the same. This is because boiling, like melting, occurs at a fixed temperature for a pure substance. So long as it is pure, boiling water cannot get hotter than 100 degrees Celsius no matter how much you heat it.
This clip is from:
First broadcast:
11 October 2007

Classroom Ideas

This clip could be used to reinforce the factors and variables that are necessary to conduct a fair test. This clip is also useful for topics about materials and reversible and irreversible changes. After watching the clip, a discussion could be held regarding boiling and evaporation and then an evaporation competition, where the children could choose their own liquids and conditions, could be held to see who can make 25ml of a liquid evaporate the quickest.

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