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Magnetism
Chatfield Senior High
Department of Physics
Magnetism Definition

Property of spin of
electrons in
magnetic substances
 Permanent: (iron)
Magnetite
Alnico
Magnetism can also
be created by a
electric current
Electromagnet
Earth’s Magnetic Field
Magnetic Field Line Rules

Field lines go from
North to South
 Field is strongest at
the poles
 No magnetic
monopoles in nature
Attraction and Repulsion of Magnets

Like poles repel

Unlike poles attract
Right Hand Rule

Thumb points in direction of conventional current
flow (+ to -)
(Note this is different than electron flow which goes from – to + (Thanks
Ben Franklin!)

Fingers point in direction of the magnetic field
Right Hand Rule (Current going left)
Right Hand Rule (Current going right)
Magnetic Field Through a Curved Wire

Magnetic north is determined by the thumb,
fingers encircle the direction of the current
Application (Solenoid)
Current Flow through two parallel wires

Current flows in
same direction
(attraction)

Current flows in the
opposite direction
(repulsion)
If a current is flowing to the right in an
uninsulated wire, the magnetic field is…
A. Going clockwise
 B. Going counterclockwise
 C. Going straight up
 D. Cannot tell from the information given

The answer is A
If current goes clockwise through a
solenoid, the north magnetic field points….
A. To the right
 B. To the left
 C. Upward
 D. Cannot tell from the information given

The answer is A
If current is traveling the same direction in two
uninsulated parallel wires, the wires…
A. Attract
 B. Repel
 C. Remain the same
 D. It is unpredictable

The answer is A
Motors

Transfers electrical energy to mechanical
energy
Parts of a Motor

Commutator
Armature
Magnet
Wires
Commutator for AC and DC Circuits
Left Hand Rule for Motors
The Alternator
Generator

Takes mechanical energy and transforms it
into electrical energy
Speaker

Try to describe how a speaker works
Speaker
Permanent magnet
 Coil of wire wound around the magnet
 AC current goes through a coil and it
causes the cone to vibrate

Microphone

Now can you explain how a microphone
works? (Hint: It is the opposite of a speaker)
Tape Recorder / VCR
Transformers!

Robots in Disguise!
Electrical Transformers!
Power Transmission
How transformers work



Power is constant in
both coils
You must have AC
source for a transformer
Transformers can be
step up (increases the
voltage) or step down
(decreases the voltage)
Transformer Equation


P = VI
Power of primary coil = Power of secondary
 Pp=Ps
 V p I p = V s Is
 V p =I s = N p
Vs IP Ns
Voltage is indirectly related to current and
directly related to the winding of wires
Transformer Problem

What is the current and the number of winding of wires
in an electrical train set?

V p =120 V
Vs=6V
N p =1000 windings I p = 1.5 A
V I =VI
(120) (1.5) = 6 I
I= 30 A (or 20 times more)
The number of windings goes down by a factor of 20 or
50 windings in the secondary coil
Tokamak
Princeton Plasma Physics Lab
Yamanashi Maglev Train