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5.2.4Electricity and Magnetism

The Earth’s Magnetic Field

5 min read 4 parts Lesson 27 of 30 1 quiz

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Section 1 of 4The Earth as a Magnet

5.2.4 The Earth's Magnetic Field
Magnetic field
  • The Earth behaves like a giant bar magnet, with a magnetic field that extends from the planet into space.
Magnetic poles
  • The geographic North Pole is close to a magnetic south pole, and the geographic South Pole is close to a magnetic north pole.
Compass direction
  • The north-seeking pole of a compass needle is attracted to the magnetic south pole near the geographic North Pole,
    • so it points roughly north.
Origin of the field
  • The field is thought to be produced by convection currents of molten iron and nickel in the Earth's outer core.

Section 2 of 4Features of the Field

Features of the Field
Field lines
  • Field lines emerge near the geographic South Pole and re-enter near the geographic North Pole, running from south to north inside the Earth.
Strength
  • The field is strongest near the poles, and near the equator the field lines are roughly horizontal and weaker.
Shielding
  • The field deflects charged particles from the Sun, which helps protect living things from harmful radiation.
Local interference
  • Magnets, iron objects and electric currents nearby can deflect a compass needle and give a misleading reading.

Section 3 of 4Compass Investigation

1
Place a plotting compass on a flat, non-magnetic surface, away from magnets, iron objects and electrical currents.
2
Allow the needle to settle, and mark the direction in which its north-seeking pole points.
3
Repeat the test at several points, and show that the needle consistently points in roughly the same direction.
4
Compare the result with a map to conclude that the compass points roughly towards the geographic North Pole.

Section 4 of 4Exam Checklist & Tips

5.2.4 – Key Points for the Exam

  • Geographic pole The point where the Earth's axis of rotation meets its surface.
  • Magnetic pole A region where the Earth's magnetic field lines enter or leave the surface.
  • Outer core The liquid layer of the Earth beneath the mantle, made mainly of iron and nickel.
  • Convection current A movement of a fluid caused by differences in temperature, which can generate a magnetic field in the outer core.
  • Plotting compass A small magnet on a pivot that shows the direction of a magnetic field.

Common Mistakes

  • Saying the magnetic North Pole is exactly at the geographic North Pole; the two are close but not the same.
  • Stating that a compass needle points to the Earth's magnetic north pole, without noting its north-seeking pole is attracted to a magnetic south.
  • Claiming the Earth's core is solid iron throughout; the outer core is molten.
  • Forgetting that nearby magnets or currents can change the reading of a compass.
Transformer Golden Equations Physics Standard

Transformer Turns Ratio & Efficiency

Ratio: Vp / Vs = Np / Ns = Is / Ip

  • Step-up reduces grid thermal loss (P = I2R).
  • Laminated core prevents eddy currents.