Transcript Chapter 19 - Magnetism and Electromagnetism

Chapter 19 - Magnetism
and Electromagnetism
Over 2,000 years ago - an area of
Greece known as Magnesia was
noted for unusual rocks
The rock, allowed to swing on a
string always pointed the same
way - towards the north star
(leading star or load star)
Magnetic rock (loadstone) contains
iron
N – north seeking pole
S – south seeking pole
Like poles repel
Opposite poles attract
Magnetic fields are created by a
moving charge.
The spinning of an electron (like
a top) creates a tiny magnetic field.
Most electrons are paired into
orbitals and spin in opposite
directions so their magnetic fields
attract.
When two opposite magnetic fields
combine they cancel each other out.
Requirements for something
to be magnetic
– It must have unpaired electrons
– The unpaired electrons must spin in the
same direction so the magnetic fields add.
– Iron, nickel and cobalt all have unpaired
electrons and can be magnetized.
Magnetic domain – a region where the
unpaired electrons spin the same
direction so their magnetic fields add.
In a magnetized material the domains
are arranged in the same direction.
see photo of magnetic domain walls
Iron materials can be temporary
magnets by an imposed magnetic
field.
In picking up paperclips with a
magnet, the paperclips become a
temporary magnet.
The Earth is a giant magnet
It contains molten iron and nickel at the
core. (not fully understood)
Geographic north – the point around which
the earth rotates. (Is the north of maps)
Magnetic north – the point on the earth that
the compass points to.
Magnetic declination – the difference in
degrees between true north and magnetic
north
It is very little (about zero) in this area
Van Allen Belts – two doughnut
shaped regions far above the earth
(1,000 to 25,000 km) that contain
high speed protons and electrons
Solar wind – a stream of electrically
charged particles that comes from the
sun.
Magnetosphere – the earth’s magnetic
field as shaped by the solar wind.
Northern lights – caused by charged
particles from space entering the earth’s
magnetic field (magnetosphere)
The earth makes magnets
Molten rock that contains iron becomes
magnetized by the earth as it hardens.
Studying ancient volcanic rock gives a
history of the earth’s magnetic field.
It moves over time and even reverses
itself every million years or so.
Electric current – a movement of
charged particles (such as
electrons moving through a wire)
A moving charge creates a
magnetic field.
Amp – a measure of current
(electron flow per second)
Solenoid – a coil of wire that produces a
magnetic field when electricity is run
through it.
http://webphysics.davidson.edu/applets/BF
ield/Solenoid.html
http://www.solenoids.com/
Solenoid + iron core makes an
electromagnetic