Magnetism and Electricity The Earth’s Magnetic Field
The Earth’s core contains a circulating liquid of molten iron and nickel. This circulation creates a large magnetic field around the planet. This field is at its strongest at the geographic north and south poles.
The Earth behaves as if there is a huge bar magnet going through its centre. The magnetic poles run in the opposite direction to the geographic poles. This is why a compass points north – its north pole is attracted to the magnetic south pole.
Geographic north pole Magnetic field lines F Have you ever n
wondered how birds know which direction to fly in when they migrate? The answer may be in their beaks. The nerve branches in their upper beaks contain lots of iron, which scientists think they use to measure the strength and direction of the Earth’s magnetic field. This is known as a biological magnetometer.
18.1
Learn more about the Earth’s core in Earth and Space 22.1
Fig. 18.1.5
The geographic north pole is near to the magnetic south pole and vice versa The Earth’s magnetic field is very important for:
z Navigation: compasses rely on their attraction to the magnetic poles to give us geographic directions.
z Protection: the Earth’s magnetic field protects the planet from large streams of energy from the Sun called solar winds. Without it, these winds would strip away the ozone layer surrounding the planet, which protects us from harmful ultraviolet radiation.
The Earth’s magnetic field deflects cosmic rays towards the north and south poles. Here, they cause the atmosphere to glow in beautiful colours known as aurorae.
Learn more about the Earth’s atmosphere in Earth and Space 22.4
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Fig. 18.1.6 The Northern Lights, aurorae borealis
