Science: Technoquest - Microwaves/Killer dolphins/Flat top clouds/Pyra mids

Questions for this column may be submitted via e-mail to sci.net@campus .bt.com

Q If you put a cup of water and a cup of maple syrup in the microwave at the same time, and for the same length of time, why does the maple syrup get hotter?

Two things affect how fast a material heats up in a microwave: its heat capacity and its radiation density. The heat capacity is defined as the amount of energy required to make a specific amount of the material rise in temperature by one degree Centigrade.

Assuming the microwave spreads its energy equally to two equally filled cups, the syrup must have a lower heat capacity than water, since it's warmer. That's not a safe assumption, though. Microwave ovens don't impart a one-off blast of energy to food - so the radiation density of the material also matters.

A microwave oven works by emitting high-energy wavesinside its cooking space. The waves bounce off the walls, and sometimes hit the food. If they come in contact with the food, some waves will be reflected and some will pass into the material. Inside the food, the microwaves lose energy, due to the presence of the material. The wave loses energy due to the contact with the material: some energy is translated into heat in the material. If some of the wave's energy passes through the material it behaves like the other waves, bouncing off the walls again until it hits food again and loses some more energy, until it is completely gone.

Now imagine you were swimming through water, and then through syrup. You will lose much more energy swimming through the syrup than the water. The energy you lose has to go somewhere - specifically, to the material you're swimming through. Swim equal distances through the water and the syrup, and the syrup ends up warmer.

If we assume the waves are equally distributed through the microwave oven, the waves will travel the same distance through the water as the syrup, but losing more energy to the syrup - which ends up hotter.

Q Can dolphins kill sharks?

Yes. Sharks don't have any bones in their bodies but are made up of cartilage, which is very flexible. Dolphins have very strong noses, which they can ram into the shark's body to cause haemorrhaging. The shark then bleeds internally until it dies.

Q How big is the Great Pyramid in Egypt?

The Pyramid of Cheops, also known as the Great Pyramid, is 147 metres high with base sides 230.4 metres long.

Q Why do some clouds have flat tops?

Some times the atmosphere can have several "layers" in it where winds travel at different speeds. If the tops of large cumulus clouds reach a layer where the wind is travelling faster than in the layer below, the tops of the clouds will be sheared off. This is called a castellate texture.

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