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ELECTRICITY & MAGNETISM
Objectives: After completing this
module, you should be able to:
• Provide evidence that fields exist
between objects exerting forces on
each other even thogh the objects are
not in contact
Magnetism
Since ancient times, certain materials, called
magnets, have been known to have the property of
attracting tiny pieces of metal. This attractive
property is called magnetism.
S
Bar Magnet
S
N
N
Magnetic Poles
Iron
filings
N
The strength of a magnet is
concentrated at the ends,
called north and south
“poles” of the magnet.
S
A suspended magnet:
N-seeking end and
S-seeking end are N
and S poles.
W
N
S
N
Bar magnet
S
N
E
Compass
Magnetic Attraction-Repulsion
S
S
N
N
N
Magnetic Forces:
Like Poles Repel
S
S
N
N
S
Unlike Poles Attract
Magnetic Field Lines
We can describe
magnetic field lines
by imagining a tiny
compass placed at
nearby points.
The direction of the
magnetic field B at
any point is the same
as the direction
indicated by this
compass.
N
S
Field B is strong where
lines are dense and weak
where lines are sparse.
Magnetic Field
The area in which magnetic forces act
The magnetic field is strongest near the
poles
Field Lines Between Magnets
Unlike
poles
Attraction
N
S
Leave N
and enter S
N
Like poles
The magnetic fields
combine to form a
stronger field
between the
magnets when
unlike poles are
near each other
Repulsion and a weaker field
N
when like poles are
near each other
Properties of a Magnet
- Attract or repel other magnets
- When allowed to swing freely one end
will point magnetic north
- Attract iron
MAGNETISM
Invisible force of “push” or “pull” by an object with
this property
Wagon does not move;
forces are not lined up
Hi! We’re e- (electrons)!!!
We usually speed around the
outside of the nucleus
In these atoms, each e- is
going its own way
Wagon moves;
forces are lined up
But in a magnet or a metal, we can
line up to become magnetic
Lined up atoms/
electrons=Domain
Inside a magnet
► -The
smallest particle of an element is an
atom
► -Atoms contain positively (protons) and
negatively (electrons) charges particles
► Spinning electrons produce magnetic fields
► In magnets, the spinning electrons are
aligned in domains that are in the same
direction
MAGNETS
Materials whose atoms can be aligned
Elements that can be magnetic
1. Fe: Iron
soft iron loses magnetism easily
2. Co: Cobalt
used to harden tools
3. Ni: Nickel
used to make jewelry
Other magnets:
1. Compass
2. Earth
MAGNETS
Domains
1. Have domain (lined up atoms)
2. Have polarity (characteristic of
magnetism)
North-seeking pole (“normal”)
South-seeking pole (“reversed”)
3. Cannot have only 1 pole
*** magnetic poles cannot be isolated***
4. Like poles repel; Opposite poles attract
MAGNETIC FIELDS
An area where the force exists; area where force is felt
Magnetic field lines
1. Leaves north pole & enters
south pole
2.
Lines closer together =
stronger field
NOTICE
1. Strongest at the poles
2.
Field lines start at the
NORTH pole and travel
towards the SOUTH pole
Temporary Magnets
► Some
materials like steel or iron can be
easily magnetized, but lose their
magnetism quickly. A magnet that easily
loses its magnetism is called a temporary
magnet
Earth is a Magnet
►A
compass will point
to magnetic north
because a compass
needle has a
magnetized needle
that spins freely.
Destroying Magnets
► When
the magnetic
domains are forced
out of alignment,
magnets will be
destroyed. This can
happen by heat or
even a violent strike
to a magnet with a
hammer
ELECTROMAGNET
A magnet with a field produced by an electric current
Electromagnetism
a moving charge (electricity)
produces a magnetic field
►
More coils of wire=
more current =
stronger magnet
►
Bigger battery/stronger
current =
stronger magnet
Solenoids
► The
magnetic field produced by a current
has three distinct characteristics:
 the field can be turned on/off
 have its direction reversed
 have its strength changed.
► Solenoid:
A coil of wire with a current. The
two ends act like magnetic poles
► A solenoid with a ferromagnetic core is an
electromagnet
ELECTRIC FIELDS
A force field that fills the space around electrical
charges
Electrical field
two charges are separated
►
vectors (lines of force) point
towards negative charges and
away from positive charges
►
strength of field (magnitude)=
distance between two charges
►
closer particles = stronger field
CONDUCTORS
A material, usually a metal, through which electrons
can flow
►
good conductor
electrons able to move
freely within the atoms of
the material
►
poor conductor or insulator
electrons are not free to
move about the atoms of
the other material
ELECTRIC CIRCUIT
A path that allows electrons to flow from negative to
positive
ELECTRICITY  MAGNETISM
Electric currents cause magnetism
►
How can you tell?
Compass needle moves when
near electrical current creating an magnetic field
MAGNETISM  ELECTRICITY
Moving magnet can generate electricity
►
How can you tell?
Electromagnetic induction
moving a magnet in and out of a
coiled wire created an electrical
current without a battery
Increasing the Strength of
electromagnets
► 1.
increase the
current in the
solenoid
► Add more loops of
wire to the solenoid
► Use a stronger
ferromagnetic
material