Reading Earth by Its Magnetism: teacher key

Magnets, grade 12 edition, written for 12th grade and up. What magnets are, how they are made, and what Earth's changing field says about the planet.

Read the book. Print this page for the key.

Questions and answers

1. Why does gravity have no poles?
   • Its pull is too small
   • The gravity from every part just adds together (answer)
   • It only acts on iron
2. What happens above the Curie temperature?
   • Long-range ordering in the material breaks up (answer)
   • The magnet doubles
   • The poles swap
3. What drives a Maglev train?
   • The powered guideway (answer)
   • A steam engine
   • A battery of iron
4. Why do scientists rely on indirect evidence about Earth's field?
   • Direct observations extend back only a few centuries (answer)
   • Earth's field never changes
   • Compasses are banned
5. What do the fossils from the last major reversal show?
   • No big changes (answer)
   • A mass extinction
   • New oceans

Words

• ferromagnetic: strongly magnetic
• convection: heat-driven flow
• declination: compass angle
• magnetosphere: magnetic shield