Download Electromagnetism - Physical Science

Magnetism(Review)
Magnetic Field Lines always move
out of the __________end of a
magnet!
A.
B.
C.
D.
East
North
South
West
Magnetic Field Lines always move
into the __________end of a
magnet!
A.
B.
C.
D.
East
North
South
West
Where are all magnets the
strongest?
A.
B.
C.
D.
At the North Pole
At the South Pole
At both Poles
Directly in the center
Magnets can be made of iron,
_________, or nickel.
A.
B.
C.
D.
Copper
Carbon
Cobalt
Cadmium
Two similar poles of a bar magnet
will always _____________.
A. attract
B. repel
Two opposite poles of a bar magnet
will always _____________.
A. attract
B. repel
Electromagnetism
--the relationship b/w electricity
and magnetism
Is there a relationship
between electricity
and magnetism? Let’s
see what I
discovered!!!
Hans Christian Oersted
Oersted’s Law
• The flow of electricity through a wire conductor
produces a magnetic field around the wire.
Right Hand Rule
• The direction of the current determines the
direction of the magnetic field.
Can anything
affect the
strength of a
magnetic field?
2 things affect the strength of a
magnetic field:
• Amount of current • # of coils of wire
– Increase current =
increase strength
– Decrease current =
decrease strength
– More turns of wire =
more strength
– Less turns of wire = less
strength
I was just
wondering what
would happen if I
slammed an iron
core through a
current carrying
coil of wire?
What did
you find
out?
If you take an iron core and insert
it into a coil of current carrying
wire, you have a temporary
magnet called an electromagnet!!
Strength of an Electromagnet
• 2 things affect the strength of an
electromagnet(same 2 things that affect the
strength of a magnetic field):
1. Amount of Current
2. # of turns of wire(# of coils)
What happens to the strength of an
electromagnet if the current through
the wire increases from 4 A to 9 A?
A. Remains the same
B. Increases
C. Decreases
Which electromagnet will be the
strongest?
A
B
Uses of Electromagnets
•
Electric Meters: because of their ability to detect
current(only work when there is one),
electromagnets are used in a variety of electric
meters.
1. Ammeter—measures current
•
Wired in series
2. Voltmeter—measures voltage
•
Wired in parallel
3. Galvonometer—”detects” current
Uses of electromagnets(cont.)
• Motors
– Use electromagnets to convert electrical energy into
mechanical energy
– An electromagnet turns inside a permanent magnet
Motors
If current moving
through a wire
produces a
magnetic field, I
wonder……
….What would
happen if we move a
wire through a
magnetic field
I bet it has never
been tested. Let’s
try it!!!
I’ll try
anything
once!!
Haven’t we
already done
that?
Joseph Henry
Michael Faraday
Faraday and Henry discovered
that moving a wire through a
magnetic field, or moving a
magnetic field through a coil
of wire “induced” a current on
the wire!!
Electromagnetic Induction—
process in which moving a
wire through a magnetic field
produces a current on the
wire.
….produces a current on a wire.
“Did we just “create” electricity”
• Generators—use electromagnets to convert
mechanical energy into electrical energy.
Generators
Other Uses of electromagnets:
Transformers
Not this Kind!!!!
Are you talking
about me?
Alternating vs. Direct Current
Alternating Current
• Current alternates, one
direction, then the other.
Plug it in, Plug it in!!
Direct Current
• Current only goes in one
direction.
Transformers
•Used to increase or decrease
the voltage of alternating
currents.
Transformers
• Consist of 2 coils of wire.
– Primary Coil
• Alternating current enters
– Secondary Coil
• Alternating current leaves
• It’s the difference in the number of turns of
wire on each coil that causes the voltage the
change.
2 Types of Transformers
• Step-up Transformer
– Increase voltage
– Secondary more turns
than primary
• Step-down Transformer
– Decrease voltage
– Primary more turns than
secondary
Math of a Transformer:
A step-up transformer has 400 turns on its primary coil
and 600 turns on its secondary coil. If the primary coil is
supplied with 120 V of alternating current, what will be
the secondary (output) voltage?
ns= 600 turns
np= 400 turns
Vs= ?
Vp= 120
Example #2
Example #3