Transcript Slide 1

Electric generators
 Television sets
 Cathode-ray displays
 Computer hard drives
 Compass

Polarized-magnets are polarized. They
have two distinct and opposite ends.
 North pole and South pole
 Like electric charges, likes repel and
opposites attract
 However, charges can be separated
magnetic poles cannot.

 The
Earth itself is a large magnet.
 The north end of a compass
needle (a magnet) points to the
geographic north pole.
 The geographic north pole is the
magnetic south pole

A magnet can cause another metal to
become polarized and have magnet
properties.
Because of the microscopic nature of
the material it keeps the magnetic
properties
 ALNICO V-a permanent magnet alloy
aluminum, nickel, and cobalt
 Rare earth elements neodymium and
gadolinium produce very strong
permanent magnets for their size

Magnetic forces can be describe by the
existence of a field around the magnet
 Much like gravitational and electric fields
 Can be non-contact forces
 Magnetic fields are vector quantities
that exist in a region in space where a
magnetic force occurs.

Magnetic field lines are imaginary lines used to
help visualize a magnetic field.
 Direction of field lines are defined as the
direction that a compass points when placed in
the magnetic field.
 Outside the magnet field lines leave the
magnet from the north pole and end the south
 Inside the magnet from south to north to form a
closed loop.

The number of field lines passing through
a surface is the magnetic flux
 The flux per unit area is proportional to
the strength of the magnetic field.

In 1820, Danish physicist Hans Christian
Oersted experimented with electric
currents in wires.
 Found that when a current was in a wire
a compass needle rotated until it was
perpendicular to the wire.
 If the compass needle rotated it must
have been because of a magnetic field.


Circular line indicate that magnetic field
lines around a current carrying wire for
closed loop in the same way that field
lines about a permanent magnet for
closed loops.
A method to determine the direction of
a magnetic field relative to the direction
of conventional current
 Pretend to hold the wire with your right
hand
 Point you thumb in the direction of
conventional current
 Your fingers point in the direction of the
magnetic field.

A long coil of wire consisting of many
loops is called a solenoid.
 The field of each loop adds to the fields
of the other loops and creates a greater
total field strength.

A method used to determine the
direction of the field produced by an
electromagnet relative to the flow of
conventional current.
 Curl your right hand fingers around the
loops in the direction of the conventional
current
 Your thumb points toward the north pole
of the electromagnet

Electrons in an atom acts like a tiny
electromagnet
 Domain is when the magnetic fields of
the electrons in a group of neighboring
atoms are all aligned in the same
direction
 When a piece of iron is not in a
magnetic field the domains point in
random directions and their magnetic
fields cancel each other out.



In the case of a
temporary magnetic
and external
magnetic field aligns
the domains and
when the external
magnetic field is
removed the domains
return to their random
arrangement
In a permanent
magnet the iron
keeps the domains
aligned after the
external magnet is
removed.