Science: Technoquest

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Q How is the Earth's magnetic field produced?

The current understanding is that the Earth's magnetic field is produced by a complex system of electric currents circulating in the molten part of the Earth's iron core - not all of which is molten. Because molten iron is a good electrical conductor, and the core is undergoing convective stirring (as its heat passes to the upper mantle), that generates currents.

Those currents produce a magnetic field just like a standard wire electromagnet, but the picture is complicated because the Earth's field interacts with the currents themselves, thus changing the convection pattern.

Inside the core, then, the magnetic field is extremely complicated, but fortunately the net effect seen from the outside is not so complicated. Measured at the surface, the Earth's field is rather like that from a slowly wobbling bar magnet. This is why the direction of magnetic north changes slowly with time.

Q How is ozone produced in the stratosphere?

First, molecular oxygen (consisting of two oxygen atoms joined by a covalent bond) is broken up by ultraviolet radiation. The individual oxygen atoms then combine with other oxygen molecules to form O3.

If you go too high in the atmosphere, there are not enough molecules for the oxygen atoms to form ozone; too low, and there is not enough ultraviolet light to break up significant amounts of molecular oxygen, as reactions in the atmosphere above have absorbed it.

If the stratospheric "ozone layer" gets thinner, more ultraviolet light gets through to the ground, which is dangerous to life. At ground level, ozone is not useful: it is very chemically reactive and does not rise to the upper atmosphere as it reacts and produces more stable compounds long before reaching it.

Q What is the equation for the Mandelbrot plot?

The Mandelbrot fractal set is given by the iterative equation Zn+1 = Zn2 + c where z and c are allowed to assume complex values such as 2 + i. (i is the (imaginary) square root of -1.)

Q How does the sulphur dioxide emission of smokeless fuels compare with that of coal?

Generally speaking, smokeless fuels are made with less sulphur in than ordinary coal. This means they will produce less sulphur dioxide when they are burnt, and so should contribute less to acid rain and similar effects.

The Technoquest website is at http://www.sciencenet.org.uk