Why this chapter matters for UPSC: Magnets and electromagnetism underpin generators (power production), electric motors (EVs), MRI machines (healthcare), and navigation. Earth's magnetic field protects life from solar radiation — relevant for space weather and satellite operations (GS3 science-tech).

PART 1 — Quick Reference Tables

Properties of Magnets

Property Description
Attracts magnetic materials Iron, cobalt, nickel are attracted
Two poles (N and S) Every magnet has a North and South pole; poles cannot be separated
Like poles repel N–N or S–S repel each other
Unlike poles attract N–S attract each other
Can induce magnetism Iron temporarily becomes magnetic when placed near a magnet
Loses magnetism When heated, hammered, or dropped repeatedly

Types of Magnets

Type Description Examples
Natural magnet Found in nature; magnetite (Fe₃O₄) Lodestone
Temporary magnet Acts as magnet only when current flows Electromagnet
Permanent magnet Retains magnetism permanently Bar magnet, horseshoe magnet, compass needle

PART 2 — Notes

Earth's Magnetic Field

Key Term

Earth's magnetic field (Magnetosphere): Earth behaves like a giant bar magnet. The magnetic field is generated by the movement of molten iron-nickel in the outer core (dynamo effect).

The magnetic poles are not exactly at the geographic poles — they shift slowly over time (magnetic pole migration).

Importance of Earth's magnetic field:

  1. Protects from solar wind: Deflects charged particles from the Sun (solar wind) that would strip away the atmosphere — this is why Mars (no magnetic field, lost its atmosphere) is barren while Earth thrives
  2. Navigation: Compass needles align with Earth's magnetic field (N pole points toward magnetic north)
  3. Bird migration: Many migratory birds (including Amur Falcons that pass through Nagaland) use Earth's magnetic field for navigation
  4. Aurora Borealis/Australis: Where solar wind particles funnel along magnetic field lines into polar atmosphere — create spectacular light displays

Electromagnets — Technology Connection

UPSC Connect

UPSC GS3 — Electromagnet applications:

When electric current flows through a coil of wire wound around an iron core → temporary magnet (electromagnet).

Applications:

  • Electric generators: Rotating magnets near coils → induces current (electromagnetic induction — Faraday's law) → basis of ALL electricity generation (thermal, hydro, wind, nuclear plants all use this principle)
  • Electric motors: Current in coil in magnetic field → rotational force → powers EVs, fans, compressors
  • MRI (Magnetic Resonance Imaging): Extremely powerful superconducting electromagnets; used in medical diagnosis; India has ~5,000+ MRI machines
  • Maglev trains: Electromagnetic levitation lifts train off tracks → no friction → speeds of 600 km/h+; China has commercial maglev; India exploring high-speed rail with electromagnetic components
  • Speakers and microphones: Vibrating coil in magnetic field
  • Crane magnets: Scrapyards use large electromagnets to lift iron/steel

India's context: India's shift to EVs (Electric Vehicles) means growing demand for permanent magnets (used in EV motors) — made from rare earth elements like neodymium and dysprosium. China controls ~85% of rare earth processing. India is working on domestic rare earth extraction (Kerala's monazite sands) as part of the Critical Minerals Mission.

Compass and Navigation

A compass uses a freely suspended magnetic needle that aligns with Earth's magnetic field:

  • N pole of compass needle points approximately toward Earth's geographic north (magnetic north is slightly different — this difference is called magnetic declination)
  • Used by sailors, mountaineers, military
  • Replaced by GPS for most modern navigation — but GPS satellites can be jammed or disrupted; compass remains important for military and emergency navigation

Exam Strategy

Prelims traps:

  • Magnetic south pole of Earth is geographically near the North Pole (confusing naming — the geographic north pole attracts the compass N pole, so it must be a magnetic south pole)
  • Magnetic poles cannot be separated: Cut a magnet in half → two complete magnets, each with N and S poles
  • Electromagnet = temporary magnet; requires current; loses magnetism when current stops
  • Aurora occurs near polar regions (where magnetic field lines dip into atmosphere)
  • Magnetite (Fe₃O₄) = natural magnetic mineral (lodestone) — different from iron oxide rust (Fe₂O₃)

Previous Year Questions

Prelims:

  1. When a bar magnet is cut in half, the result is:
    (a) One north pole and one south pole piece
    (b) Two complete magnets each with north and south poles
    (c) Two demagnetised pieces
    (d) One magnet with double strength

  2. Earth's magnetic field is primarily important for life because:
    (a) It causes tides
    (b) It creates the seasons
    (c) It deflects harmful charged particles (solar wind) away from Earth
    (d) It enables photosynthesis

  3. An electromagnet differs from a permanent magnet in that it:
    (a) Requires electric current to maintain its magnetic properties
    (b) Has only one pole
    (c) Cannot attract iron
    (d) Is made of copper