Magnetism: Concepts, History, and Earth's Magnetic Field
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47 Terms
What is magnetism?
Force of attraction or repulsion between magnetic poles.
Where does the term 'magnetism' come from?
Magnesia, an ancient district in Greece.
What were lodestones?
Natural stones that attracted iron.
Who first used magnets as compasses?
The Chinese in the 12th century.
What happens between opposite magnetic poles?
They attract.
What happens between like magnetic poles?
They repel.
What two factors affect magnetic force strength?
Distance between magnets and magnet strength.
Magnetic field lines leave which pole?
North pole.
Magnetic field lines enter which pole?
South pole.
What does it mean when field lines are close together?
Stronger magnetic field.
Where is a magnet's field strongest?
At the poles.
Can a single magnetic pole exist by itself?
No.
What happens if a magnet breaks in half?
Each piece forms new north and south poles.
Where are the poles on a bar magnet?
At both ends.
Where are poles on a horseshoe magnet?
At the ends of the U shape.
What causes magnetism?
Motion/spinning of electric charges.
How do electrons contribute to magnetism?
Their motion creates electric current and acts like tiny magnets.
Electrons move around what part of the atom?
The nucleus.
What are magnetic domains?
Regions where atomic magnets align in the same direction.
What happens to domains when a material becomes magnetized?
Domains align.
What shape do magnetic fields make around a current-carrying wire?
Concentric circles.
What happens to magnetic field direction when current reverses?
Field direction reverses.
What is an electromagnet?
Iron core placed inside a current-carrying coil.
How does an iron core strengthen an electromagnet?
Domains align and increase the field.
What type of coils make the strongest electromagnets?
Superconducting coils.
Name one use of electromagnets.
Lifting cars and iron objects.
What train technology uses electromagnets?
Maglev trains.
Electromagnets control what in accelerators?
Charged-particle beams.
What happens to moving charges in magnetic fields?
They experience a deflecting force.
When is magnetic force greatest?
Motion perpendicular to field lines.
When is magnetic force zero?
Motion parallel to field lines.
When is magnetic force least?
Motion at angles other than perpendicular.
What creates Earth's magnetic field?
Moving molten iron core.
Is Geographic North the same as Magnetic North?
No.
How many magnetic reversals occurred in the last 5 million years?
About 20.
What happens during magnetic reversal?
Earth's magnetic field changes direction.
What causes auroras?
Charged particles entering Earth's atmosphere.
Name the northern lights.
Aurora borealis.
Name the southern lights.
Aurora australis.
What are cosmic rays?
Charged particles from space.
Why are cosmic rays dangerous?
They are hazardous to astronauts.
What protects Earth from many cosmic rays?
Earth's magnetic field.
What are Van Allen radiation belts?
Trapped charged particles around Earth.
What mineral do magnetotactic bacteria produce?
Magnetite.
Why do bacteria use magnetite?
As internal compasses.
How do pigeons use Earth's magnetic field?
Navigation and latitude detection.
Name animals with magnetic sensing abilities.
Pigeons, bees, butterflies, sea turtles, fish.