DK - WOW! The Visual Encyclopedia of Everything

The red needle on this compass points to the

magnetic north pole

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LODESTONE

Nearly 3,000 years ago, people discovered that a strange type of rock could attract iron objects. This rock, called lodestone or magnetite, is a form of iron oxide with strong natural magnetism. The first compasses were made from lodestone.^6

MAGNETIC SCAN

In a magnetic resonance imaging (MRI) scan, a patient is placed in a magnetic field and radio waves are passed through the body, causing molecules within body tissues to vibrate. Different tissues vibrate in different ways, allowing each part to be seen clearly.

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MAGNETIC EARTH

Electric currents circulating inside Earth as the planet rotates cause it to act like a giant magnet, with a magnetic field that extends thousands of kilometres into space. Earth has magnetic poles, which are near, but not the same as, the geographic North and South Poles.^8

COMPASS

In use from around the 12th century, a compass contains a magnetic needle, which is free to rotate on a pivot. The compass needle will always align itself with Earth’s magnetic field, so that its needle points towards the magnetic north pole.

North pole

Steel pins are

attracted by the magnetic force of the lodestone

This MRI scan shows

soft tissues as well

as bones

North pole

Iron filings join because opposite poles attract

North pole

South pole

Iron filings push away because like poles repel

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108_109_Magnetism.indd 109 03/01/19 12:10 PM