Download The Earth`s Magnetic Field

Artist's view of the mid-Atlantic ridge (from World Ocean Floor by Bruce C. Heezen and
Marie Tharp, 1977) and the increasing age of rocks away from it.
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The surface of the
Earth, or crust, is made
of less dense rock
floating on a layer of
denser material.
The crust has distinct
boundaries, indicating
that the continents are
separate bodies.
Shown here is an artist
conception of one such
boundary, a mountain
range in the middle of
the ocean floor called
the Mid-Atlantic Ridge.
The Earth’s Magnetic Field
! Introduction
" The Earth acts like a magnetic as indicated by its
affect on a compass
" Magnetic forces are communicated by a magnetic
field – direct physical contact is not necessary to
transmit magnetic forces
" Magnetic field are depicted in diagrams by
magnetic lines of force
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Each line represents the direction a compass would point
Density of lines indicate strength of field
Magnetic fields also have polarity – a direction
from a north magnetic pole to a south magnetic
pole
Magnetic fields are generated either by large-scale
currents or currents on an atomic scale
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Schematic view of Earth's magnetic field lines and photograph of iron filings sprinkled
on a toy magnet, revealing its magnetic field lines.
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The Earth’s Magnetic Field
! Origin of the Earth’s Magnetic Field
" The magnetic field of the Earth is generated
by currents flowing in its molten iron core
" The currents are believed to be caused by
rotational motion and convection (magnetic
dynamo)
" The Earth’s geographic poles and magnetic
poles do not coincide
" Both the position and strength of the poles
change slightly from year to year, even
reversing their polarity every 10,000 years
or so
The Earth’s Magnetic Field
! Magnetic effects in the upper atmosphere
" Earth’s magnetic field screens the planet from
electrically charged particles emitted from the Sun,
which are often of an energy harmful to living cells
" The screening entails the Earth’s magnetic field
deflecting the charged particles into spiral
trajectories and slowing them down
" As the charged solar particles stream past Earth,
they generate electrical currents in the upper
atmosphere
" These currents collide with and excite molecules
" As the molecules de-excite, light photons are given
off resulting in Aurora
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Electrically charged particles from the Sun spiral in the Earth's magnetic field.
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Photographs of an aurora from (A) the ground (courtesy Eugene Lauria) and
(B) from space. (Courtesy NASA.)
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The Earth’s Magnetic Field
! Magnetic effects in the upper
atmosphere (continued)
Region of the upper atmosphere where
the Earth’s magnetic field affects particle
motion is called the magnetosphere
" Within the magnetosphere charged
particles are trapped in two doughnut
shaped rings that encircle the Earth and
are called the Van Allen radiation belts
" Van Allen belt particles are energetic
enough to be a hazard to spacecraft and
space travelers
"
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Artist's view of the Van Allen radiation belts (side view).
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Light and Atoms
Earth is surrounded by a magnetic
field believed to be produced by
convection in its molten iron core.
The magnetic field produced is
similar to that of a bar magnet.
The axis of the Earth’s magnetic field
differs from the axis of rotation by 11°,
placing the north magnetic pole in a
different location than the geographic
(true) North Pole.
The Earth’
Earth’s Magnetic Field Protects us
from the Solar Wind
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