Transcript Magnetic Fields - Rainier Connect

Magnetic field (B-field) of a
bar magnet
Magnetic field of Earth
Notice that
the “North”
pole of the
Earth is a
magnetic
South pole!
Earth’s field
is similar to
that of a bar
magnet.
Source of magnetic field
Magnetic fields (B-fields) are
created by electrical currents
B = (2  10-7)I/R
Direction of magnetic field
around wire
The field circles or loops
around an electrical
current.
The direction of the field
is determined by a righthand rule.
Bar magnet
Inside a solid material,
currents within the
atom cause each atom
to act like a little
magnet. In some
materials, like
aluminum, the atoms
are not aligned, so no
bar magnet. In iron,
many regions
(domains) of atoms
are lined up
magnetically and thus
create a bar magnet.
Coils and currents
A current in a wire creates a magnetic
field (B-field) around the wire. If you make
a coil out of the wire, the B-fields from
each loop add up. You get a field around
the coil that looks like that from a bar
magnet!
Coils and currents - direction
The location of the North
and South poles for the
coil are determined by
another right-hand rule.
Coil acts like bar magnet
When the current is on, the coil acts like
a bar magnet (which end is North pole?)
and attracts the real bar magnet. Where
are the N and S poles for the bar?
The Earth’s
magnetic
field is
caused by
currents
within
molten rock.
Detailed
models of
what is
going on are
still being
developed.
Magnetic vs.
Electric
•Like charges repel
•Like poles repel
•Unlike charges attract
•Unlike poles attract
•Electric fields are
produced by charges
•Magnetic fields are
produced by currents
•E-fields exert forces
against charged
particles
•B-fields exert forces
against moving charged
particles (currents)
Magnetic forces on moving
charges
When a charge
moves through a
B-field, it feels a
force.
•It has to be
moving
•It has to be
moving across the
B-field
Direction of force is
determined by another
right-hand rule
Magnetic forces on moving
charges
FB = qvB
If a current I in a wire
of length L passes
through the field, the
force is:
FB = BIL
Magnetic force on current
F = BIL
Wire can be
levitated by
magnetic force
when a current
passes through it
Aurora
Caused by interaction of charged particles from
Sun with Earth’s B-field and atmosphere
Planets like
Jupiter and
Saturn have
strong B-fields
that interact
with charged
particles from
the Sun.
This is a picture of an aurora on
Saturn as seen in UV light