Transcript Magnetism - Broken Arrow Public Schools

Chapter 17

magnetism – the properties and interactions
between magnets
 based on the alignment of particles in a substance
 magnetic – the ability of an object to make forces on
magnets and other magnetic objects

three types:
 permanent magnet
 temporary magnet
 electromagnet

The earliest magnets were found
naturally in the mineral magnetite which is
abundant the rock-type lodestone. These
magnets were used by the ancient peoples as
compasses to guide sailing vessels.

material that keeps its magnetic properties
 ex: your normal understanding of a magnet – fridge
magnets,
bar magnets…etc.

material which acts like a permanent magnet
when inside of a strong magnetic field but
lose their magnetism outside of it
 paperclips, nails, other soft
iron items…etc.
 used in motors

device which changes electrical energy into
mechanical energy
 we use permanent magnets
and electromagnets to make
electric motors and generators
▪ generators turn mechanical
energy to electrical energy
 these work by changing the
direction of the electric current

helix of wire tightly wrapped around an iron
core – acts like a magnet when current is
applied to it
 strength of the magnet
varies with the current
[more current,
more magnetized]

…[review] is based on the alignment of
particles in a substance.

all atoms have moving electrical charges
[electrons]
 these moving electrons cause a magnetic field
 this causes the Faraday Effect
 Faraday Effect Clip

The magnetic field lines around
horseshoe and disk magnets are
closest together and strongest
at the magnet’s poles.

Unlike poles of magnets attract
each other

Like poles of magnets repel.


are stronger nearer to the top of magnet
create North [pull north] &
South [pull south] poles
 a pole is where the force of the magnet is the
strongest
 each pole is attracted to the other
[hence the
swirls of field
from N to S
or from S to N]
 The earth is like a
giant magnet!

The nickel iron core
of the earth gives
the earth a
magnetic field
much like a bar
magnet.
 atoms in an object behave like tiny magnets
 In an area of an object where all of the particles have a
similar magnetic field is called a domain
 the particles of most objects are not aligned

…[the particles of most object are not
aligned]
 aligning particles will cause an overall magnetic field
 the force of a magnet depends on the alignment
of its particles
Another magnet can cause the
alignment of an object’s electrons
Magnetic substances like iron, cobalt, and nickel are
composed of small areas where the groups of atoms are
aligned like the poles of a magnet. These regions are called
domains.
All of the domains of a
magnetic substance tend to
align themselves in the same
direction when placed in a
magnetic field.
These domains are typically
composed of billions of atoms.


When an electric current passes through a
wire a magnetic field is formed.

The direction of the current depends on the
directions of the current in the wire, to a
position of lower potential energy.

A galvanometer is an electromagnet that
interacts with a permanent magnet. The
stronger the electric current passing through the
electromagnet, the more it interacts with the
permanent magnet.

The greater the current
passing through the
wires, the stronger the
galvanometer interacts
with the permanent magnet.
We have seen how electricity can produce a magnetic
field, but a magnetic field can also produce electricity!
How?
What is electromagnetic induction?
Moving a loop of wire through a magnetic field produces
an electric current. This is electromagnetic induction.
A generator- used to convert mechanical
energy into electrical energy by electromagnetic
induction.
Simplest Electric Motor Clip
How does an electric motor work?
Go to the next slide 
Simple as that!!
Direct current versus alternating current –
AC vs DC : What’s the difference?
Direct current is electrical current which comes from a
battery which supplies a constant flow of electricity in
one direction.
Alternating current is electrical current which comes
from a generator. As the electromagnet is rotated in the
permanent magnet the direction of the current alternates
once for every revolution.
Go to this website and click the button for DC then for
AC to visually see the difference between the two.
You can see that the DC source is a battery – current
flows in one direction. The AC source is the generator
and the current alternates once for each revolution.