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10.3Chapter 10: The Earth in Space (Galaxies and Asteroids)

Magnetic Earth — Alhussan Physics - Stage 8 Revision Notes & Topical Questions

5 min read 7 parts Lesson 3 of 5 1 quiz

📚 Alhussan Physics - Stage 8 Hub / Topical Revision
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Lesson summary

Physics 10.3 Magnetic Earth — Earth's Core Dynamo, Magnetosphere and Auroras — Alhussan International Academy — Physics (Stages 7–9) notes: Explain what a compass does, describe the Earth's magnetic field and explain why the Earth has one.Compass = a small magnet on a pivot that …

  • Suspended magnet
  • Bar magnet
  • Magnetic poles
  • Outer core
  • Dynamo effect
  • Solar wind

Part 1 of 5The compass

1Compass
Compass a small magnet on a pivot that shows which way is north.
2Suspended magnet
  • A magnet hung on cotton lines up in the same north-south direction each time.
3Reason
  • The Earth's magnetic field exerts a force on the needle, so it lines up with the field.
4History
  • People have used compasses to navigate since ancient times, and some birds and insects use the field to navigate.

Part 2 of 5Shape of the Earth's field

Bar magnet
  • The Earth behaves as if it has a bar magnet inside it, with a field like a bar magnet's.
Magnetic poles
  • Compass needles point to the Earth's magnetic pole, not the geographic North Pole at the top of the axis of rotation.
  • The magnetic north pole is in Canada, about 400 km from the geographic North Pole.
  • It is moving at about 30 km a year from Canada towards Russia.
  • The magnetic pole near the Arctic is really a south pole of the field because it attracts the north end of a compass.
Dip
  • The field lines also go into the ground at an angle, so a magnet free to turn in three dimensions points diagonally downwards.
Dip size
  • It is small near the equator and increases towards the poles, where the field points straight down or up.

Part 3 of 5Why the Earth has a magnetic field

Why the Earth has a magnetic field
No bar magnet
  • There is no permanent magnet inside the Earth.
Outer core
  • It is made of liquid iron, with some nickel, that can move and conducts electricity.
  • Moving currents of iron in the core act like an electromagnet.
  • The movement is driven by heat from the inner core and the Earth's rotation.
Dynamo effect
  • This process of making a field from moving conducting liquid is called the dynamo effect.
Particles
  • The particles in a liquid can flow past each other, whereas in a solid they can only vibrate, so a liquid core is needed.
Reversals
  • The field has flipped in the past, with the poles changing places about 780 000 years ago, and it may happen again.

Part 4 of 5Magnetosphere and the solar wind

Solar wind
Solar wind a stream of electrically charged particles emitted by the Sun in all directions.
  • It is not wind you can feel.
  • The particles can damage or kill cells.
Magnetosphere
Magnetosphere the region around the Earth where its magnetic field deflects the solar wind, so most does not reach the surface.
Protection
  • Without the field, the solar wind would endanger living organisms.

Part 5 of 5Auroras

Aurora
Aurora the dramatic lights in the sky called the northern and southern lights.
Cause
  • Some solar wind particles are guided to the north and south poles, where they collide with atoms and molecules in the upper atmosphere.
Light
  • The collisions release energy as light.
Requirements
  • A planet with a magnetic field, charged particles from the Sun and an atmosphere.

Key terms

TermMeaning
Magnetic fieldThe region where magnetic materials experience a force.
Dynamo effectProduction of a magnetic field by moving electrically conducting liquid.
Solar windA stream of charged particles from the Sun.
MagnetosphereThe region around the Earth where its magnetic field deflects the solar wind.
AuroraLights in the sky produced by solar wind particles hitting the atmosphere.

Avoid these mistakes

1
Thinking a compass points to the geographic North Pole — it points to the magnetic pole.
2
Thinking the Earth contains a bar magnet — the field comes from moving liquid iron.
3
Thinking the solar wind is air — it is charged particles.
4
Thinking the magnetic field never changes — the poles move and have reversed.

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