How do ocean tides create magnetic fields? © Getty Images

How do ocean tides create magnetic fields?

Michael Faraday wondered if electrical conductors moving through magnetic fields might lead to a natural source of electricity- turns out it might.

Asked by: Toby Graham, Shrewsbury
We’re taught in science lessons that it’s possible to create electric current by moving electrical conductors through magnetic fields. Known as Faraday’s law of induction, it’s the basic idea behind electricity generation in power stations. But shortly after discovering the effect in 1831, Michael Faraday wondered if it might lead to a natural source of electricity. To find out, he tried to detect the current produced by the electrically conducting river water flowing through the Earth’s magnetic field under London’s Waterloo Bridge. The experiment, conducted in January 1832, was a failure, but Faraday remained convinced the currents did exist – if only extremely weakly.

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In early 2018, a trio of ESA satellites called Swarm were able to detect electric currents generated in the world’s oceans as they are dragged through the Earth’s magnetic field by the gravitational pull of the Moon. These currents are then able to induce their own feeble magnetic fields – around 20,000 times weaker than the Earth’s magnetic field. Mapping the oceans’ magnetic signature required state-of-the-art equipment unimaginable in Faraday’s time. But as well as vindicating the Victorian genius’s claim, the research is expected to provide a whole new way to monitor the movements of the oceans.

Why does every magnet have two poles, not just one? © Getty Images

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