Physics 10
⇒ Like poles
repel
Magnetism
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Magnetic Fields
⇒ Opposite
poles attract
Magnetic Fields
⇒ The magnitude
(strength) and direction
of a magnetic field are
represented by magnetic
field lines.
⇒ Magnetic field lines point from the north to the
south pole.
⇒ The closer together the magnetic field lines, the
stronger the magnetic field.
⇒ The north pole of a compass points in the
direction of a magnetic field at any point.
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Magnetic Fields
Magnetic Domains
⇒ Not all pieces of iron are magnetized because the
magnetic domains in ordinary iron are not aligned.
Opposite poles
Like poles
Exercise 18
Cans of food in your
kitchen pantry are likely
magnetized. Why?
⇒ You can induce a unmagnetized piece of iron to
become magnetized by placing it in a strong
magnetic field. Many of the magnetic domains are
then induced into alignment.
Magnetic Field from a Current Carrying Wire
⇒ Since a moving charge produces a magnetic
field, it follows that a wire with a current flowing
through it also produces a magnetic field.
⇒ Cans contain iron. Magnetic domains in
the can tend to line up with the Earth’s
magnetic field. When the cans are left
stationary for several days, the cans become
magnetized by induction, aligning with the
Earth’s magnetic field.
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Magnetic Field from Current Carrying Wires
⇒ If the current carrying wire is bent into a loop,
the magnetic field lines become bunched up inside
the loop.
⇒ As the number of loops is increased, the strength
of the magnetic field inside the loop is increased.
Electromagnets
⇒ An electromagnet is just a coil of wire
with current flowing through it.
⇒ The strength of an electromagnet can be
increased by increasing the current through the
coils.
⇒ The strength of an electromagnet can
also be increased by having a piece of iron
within the coil. The magnetic domains
within the iron are induced into alignment,
adding to the magnetic field of the coil.
The Earth’s Magnetic Field
⇒ The Earth’s magnetic field is similar to
the magnetic field from a giant bar magnet.
The Earth’s Magnetic Field
If like magnetic poles repel, why
does the north pole of a magnet
point to the Earth’s north pole?
⇒ The Earth’s geographic north
pole is actually a magnetic south
pole.
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The Earth’s Magnetic Field
The Earth’s Magnetic Field
⇒ Scientists do not know for certain what
causes the Earth’s magnetic field.
⇒ The Earth’s
magnetic north pole
and geographic north
pole are not aligned.
magnetic declination ⇒ angle between the
orientation of a compass and true north
Cosmic Rays
⇒ Scientists believe it has something to do with
electric currents deep within the Earth’s interior.
⇒ The magnetic field of the Earth is not
constant. It has decreased to zero (zero phase)
and even reversed over the years.
⇒ The Earth’s magnetic field has reversed
about 20 times during the last 5 million years.
Van Allen Radiation Belts
⇒ The universe is full of charged particles
called cosmic rays that consist of protons
and atomic nuclei.
⇒ Theses charged particles are traveling at
insane speeds and are hazardous to
astronauts.
⇒ Most of these charged particles are
deflected away from the Earth by the Earth’s
magnetic field.
⇒ Some of the charged particles become
trapped in the Earth’s magnetic field and make
up the Van Allen radiation belts.
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Magnetic Bottle
Aurora Borealis
⇒ Charged particles
trapped in the Earth’s
magnetic field bounce
back and forth between
the magnetic poles.
⇒ Charged particles can become
trapped by strong magnetic fields.
Aurora Borealis
⇒ Some of these charged particles can escape
the magnetic field and enter the Earth’s
atmosphere, creating an aurora borealis.
Aurora Borealis
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Aurora Borealis
Aurora Borealis
Aurora Borealis from Space
Aurora Borealis from Space
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