What were lodestones used for by early navigators?

• As rudimentary compasses

• As weapons

• As jewelry

• As currency

Which type of magnet requires an electrical current to generate a magnetic field?

• Electromagnets

• Permanent magnets

• Temporary magnets

• Lodestones

What is the strongest type of permanent magnet mentioned in the passage?

• Neodymium magnets

• Alnico magnets

• Ceramic magnets

• Samarium cobalt magnets

What happens to the magnetic force between two poles if the distance between them is doubled?

• It diminishes to one-fourth its former value

• It doubles

• It remains the same

• It quadruples

What is the Earth's magnetic field strength at its surface approximately?

• 0.5 gauss

• 5 gauss

• 50 gauss

• 500 gauss