Creating a magnetic field using electricity is easy: an electric current flowing in a wire generates a magnetic field around that wire.

ECONOMIST: Recreating the planet's magnetic field in a laboratory

And when a magnetic field line vibrates, he says, it makes an electric field which excites current in wires.

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Although they have not been found to cause any harm, the cables on conventional pylons, which transmit a three-phase alternating current, generate a strong electric field and a continuous buzz of low-frequency radio waves.

ECONOMIST: Monitor

Dr Benford reckons some of them could have built up an electric current as they moved through the strong magnetic field that pervades the centre of the galaxy.

ECONOMIST: Here be serpents

As the train's magnets pass over a frame, they induce an electric current in it and this, in turn, generates a magnetic field which repels the magnet that started the whole process and thus levitates the train.

ECONOMIST: Maglev trains