Science: Technoquest

Q When a bulb blows, why does the fuse sometimes blow too?

When a filament in a light bulb blows, the bulb can arc (a spark jumps from one side to the other). The lamp then becomes a discharge lamp. The discharge has little resistance (since the bulb has very little gas in it) and this draws a lot of current, blowing the fuse. This effect can be prevented by putting nitrogen in the bulb.

Q What are male and female emus called?

The male emu is the "rooster", the female is the "hen". Just-hatched babies are "chicks", 10-to-15-month-olds are "yearlings", and 16-to-23- month-olds are "coming twos".

Q What is the life cycle of the crab louse?

The female crab carries eggs under her abdomen, which resemble bunches of grapes, and are a bright orange colour when first laid. This colour then gets darker, and sometimes the eye-spots of the larva can be seen through the egg case. The larvae hatch as zoea, which look like tiny commas and can swim. After a number of moults, the zoea develop into a megalop stage, which has legs and claws, but its tail is still visible. A small appendage on the tail can help the megalop to swim. The megalop moults and changes into a small crab and the tail, instead of protruding, is now tucked under the body of the crab.

Q Do other mammals - especially primates - have monozygotic [identical] twins?

Yes, basically. For example, the nine-ringed armadillo, roe deer and coypu all have monozygotic twins.

Q How much does the cortex of the human brain weigh?

The cortex has been estimated to contain about 15 billion to 25 billion nerve cells. That is about a quarter of all the cells in the brain. But these estimates are notoriously unreliable. We do know it is about 3 millimetres thick. So if about half the brain weight is nerve cells and the rest is fibres, and if one-quarter of the cells are in the cortex, it ought to be about one-eighth of the weight of the brain. That would make it about 150-200 grams - let's say about 6 ounces.

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