MAGNETISM
INTERACTIONS BETWEEN MAGNETS
Magnets have 2 poles called North and South
 Basic rule: Like poles repel, opposite poles
attract
 What happens when we try to separate the poles
of a magnet?
 Two smaller magnets are created
 The two poles of a magnet can never be
separated

WHAT ARE MAGNETS MADE OF?

Iron, Nickel, and Cobalt are elements that are
naturally magnetic



These are called ferromagnetic materials
Objects containing these elements will interact
with magnets
They can also become magnetized
A CLOSER LOOK INSIDE MAGNETS

Iron atoms behave like tiny magnets

This is due to a property of electrons called spin


Spin is an intrinsic magnetic property of
fundamental particles
Electrons can have two values of spin, which are
called “spin up” and “spin down”
INDIVIDUAL ELECTRONS HAVE MAGNETIC POLES
WHICH DEPEND ON THE ORIENTATION OF THEIR SPIN


In atoms with many electrons, the electrons
usually occur in pairs with spins in opposite
directions
For every “spin up” electron, there is a “spin
down” electron
However, elements with an unpaired electrons
don’t necessarily form solids with magnetic
properties
 This is because individual atoms with the solid
are randomly arranged


This random arrangement produces a solid with
no magnetic properties
Non-magnetic solid
Magnetic solid
MAGNETIC DOMAINS



In a piece of iron, many iron atoms can line up
and form domains
Domain: a section inside a piece of iron where
many iron atoms are aligned
Domains are typically 0.1mm in size
Non-magnetized piece of iron:
domains are randomly aligned
Magnetized piece of iron:
Domains are aligned
MAGNETIC FIELDS


The field concept can be extended to include
magnetic forces
Magnets create fields surrounding them, other
magnets will experience forces when placed in
those fields
MAGNETIC FIELD OF A BAR MAGNET
MAGNETIZING A PIECE OF IRON


Domains within the iron will line up when placed
in an external field
When the domains line up, the piece of iron has
become magnetized


It will behave like a bar magnet
It is therefore attracted to the external magnet
MAGNETIC FIELDS



Magnetic Field lines appear to point from the
North to the South pole
They are actually continuous loops that pass
through the magnet itself
Magnetic fields strength is measured in Teslas
(T)
HOW ELECTRIC CHARGES INTERACT WITH
MAGNETIC FIELDS


Electric charges have to be moving in a magnetic
field to experience a force
Specifically, they have to be moving
perpendicular to the magnetic field to experience
a force
THE MAGNETIC FORCE ON A CHARGED
PARTICLE
F = qvB
F = force on the charge
 q = charge of the particle
 v = speed of the particle
 B = magnetic field strength


This equation only tells us the magnitude of the
force
THE DIRECTION OF THE MAGNETIC FORCE
 Use
the Right Hand Rule:
Point your fingers in the direction of the velocity
 Curl your fingers in the direction of the field
 Your thumb points in the direction of the force

EXAMPLES
EARTH AS A MAGNET
The Earth behaves like a large magnet
 Therefore, it produces a magnetic field
 The south magnetic pole is closely aligned with
the geographic north pole

Earth is like a large upside down magnet
It has a value of 2.25 x 10-5 T
 Compasses react in this field by having their
north magnetic pole attracted to earths south
magnetic pole

EARTH’S MAGNETIC FIELD
THE SOLAR WIND

The sun emits a constant stream of high energy
charged particles (protons and electrons)

Called the Solar Wind
Solar Flare
 Solar Wind


The Earth’s magnetic field acts like a shield,
deflecting most of these particles
EARTH'S FIELD 3-D



Many particles get trapped in the field and spiral
down towards the magnetic poles
They crash into the upper atmosphere, causing
the oxygen an nitrogen to glow
This is commonly know as the Auroras, or
Northern and Southern Lights
MOVING CHARGES CREATE MAGNETIC
FIELDS


A wire carrying a current creates a magnetic field
The field lines are closed loops that circle the
wire
MAGNETIC FIELD OF A STRAIGHT WIRE
Current pointing up
Current pointing into the
board
RIGHT HAND RULE #2: DIRECTION OF THE
FIELD PRODUCED BY A WIRE

The magnitude of the force is given by the
equation:
µ𝐼
𝐵=
2𝜋𝑅
COILS AND SOLENOIDS
Solenoid
Coil
SOLENOIDS



Solenoids produce magnetic fields that are
identical to long bar magnets
They have “north” and “south” poles
They will interact with each other the way bar
magnets do
FIELD OF A BAR MAGNET AND SOLENOID
MAGNETIC FIELD OF A SOLENOID



Use Right hand rule
#3
Curl fingers in
direction of I,
Thumb points in
direction of B
MAGNETIC FIELD OF A SOLENOID

The filed inside a solenoid is uniform and strong

It is given by the equation:
𝐵= µ
𝑛
𝐿
𝐼
COILS


Coils of wire create magnetic fields that are
identical to short bar magnets
These are referred to as electromagnets
MAGNETIC FIELD OF A COIL OF WIRE