Science: Technoquest

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Q Sometimes when you boil water in a microwave and then add coffee granules, you get a fizzing noise. Why?

For water to boil, or freeze, there must be nucleates in the water. These can be anything from small impurities to coffee granules that the water can boil off or freeze around. When you boil water in a pan, you get convection currents that disturb the water letting in bubbles of air for the water to boil off, which also allows the water to boil away. This doesn't happen in a microwave so the water becomes superheated (reaches above 100C without boiling). Once you add the coffee granules, the water suddenly releases all the energy it has stored up inside by boiling instantly and becoming steam. This is the fizzing noise you hear. It can be quite dangerous if the water is heated excessively or is in a container that doesn't radiate the heat away very well. There have been stories of cups of water "exploding", sending coffee granules and boiling water over the person making the coffee.

Q What are male and female emus called?

The male is the "rooster", the female the "hen". Just-hatched babies are "chicks", 10- to 15-month-olds are "yearlings" and 16- to 23-month- olds are "coming twos". When they have their own chicks they are called "proven breeders".

Q How deep can a sperm whale dive?

They are known to dive to 350m (1,150 feet) but the deepest was found tangled in cables 1,134m (3,720 feet) down.

Q Why do ice cubes go white?

When ice is made in a freezer, the freezing starts from different points within the cube, ie the crystal structure of the cube isn't uniform. When light enters it, you get refraction and reflection inside the cube so light doesn't go straight through and the cube isn't transparent.

Q Why does the voice sound different when recorded?

Normally we hear our voices through the bones in our skull. The vibrations that we hear come through our own bones. When you record your voice and play it back, it sounds different because you hear the vibrations that have travelled through the air.

You can also visit the technoquest World Wide Web site at http://www.sciencenet.org.uk

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