J. A. Gonzalez SEM Pre
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AP Physics Notes Page No.
1
Ch.
2
4
–
Magnetic Fields
2
4
.1
–
Magnets: Permanent and Temporary
General Properties of Magnets
Magnets have two sides called poles, one north
-
seeking (north pole) and one south
-
seeking
(south pole).
Polarized
: The quality of having two opposite magne
tic poles, one north
-
seeking and one south
-
seeking.
Experimentally, it can be observed that
Like poles repel each other
Unlike poles attract each other
Magnets always have two opposite magnetic poles.
Magnetism
Magnetic Force
: Force associated with th
e motion of electric charges.
Magnetic Field
: Disturbance in the region of space surrounding objects in which electric charges are
moving. It is a vector quantity that relates the force exerted on a magnet or a current
-
carrying wire to
the strength of t
he magnet or the size of the current.
Magnetic Flux
: The number of magnetic field lines passing through a given surface area.
First Right
-
Hand Rule
: Method used to determine the direction of the magnetic field around a
current carrying wire.
Magnetic
field near a coil
Solenoid
: A coil of wire with many loops that acts like a magnet when a current is allowed to flow
through it.
Electromagnet
: A current
-
carrying coil with a north and a south pole that is iteslf a magnet.
Second Right
-
Hand Rule
: Met
hod used to determine the direction of the field produced by an
electromagnet.
Ferromagnetic Materials
When you place a piece of iron, nickel or cobalt near a permanent magnet, they become
magnetic.
Ferromagnetism
: The property of a substance by which
it is strongly attracted by a magnet. [It
involves electron spin and alignment of magnetic moments in domains.]
J. A. Gonzalez SEM Pre
-
AP Physics Notes Page No.
2
Magnetic Domains
Each electron in an atom acts like a tiny electromagnet.
The magnetic fields of the electrons in a group of neighboring ato
ms combine together to form
“domains.”
Domain
: A small group, usually 10 to 1000 microns, that is formed when the magnetic fields of the
electrons in a group of neighboring atoms combine together.
2
4
.2
–
Forces Caused by Magnetic Fields
.
Forces on
Currents in Magnetic Fields
If you move a current through a wire in a magnetic field, the wire will experience an external
force.
Third Right
-
Hand Rule
: Method used to determine the direction of the force on a current
-
carrying
wire in a magnetic field.
Force on a Current Carrying Wire in a Magnetic Field
:
F = BIL
Galvanometer
: Device used to measure very small currents.
Electric Motor
: Device that converts electrical energy into kinetic energy.
Forces on a Single Charged Particle
Cathode Ray Tube
:
Electron tube that converts electrical signals into a pattern on a screen. It
consists of an electron gun which produces an electron beam that is focused onto and moved across a
luminescent screen by magnetic and/or electric fields.
It forms the basis
of the oscilloscope and TV/computer monitors.
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