Download Magnetism - Morgan Science

Magnetism
Chapter 36
What is a Magnet?

Material or object that produces a
magnetic field.

Two types:


Permanent
Electromagnet
What causes Magnetism?

In order to create a magnetic field, a
charged particle must be moving.

Moving and spinning electrons cause
magnetic fields in every object.
Domains



A small region of space where the
magnetic fields produced by moving
electrons are aligned together.
Often, the directions of the domains
cancel each other out.
Ferromagnetic material

Cancellations do not occur, resulting in a
net magnetic field
Domains
Magnetism

Opposites poles attract
Like poles Repel

Magnetic Poles can not be separated


Every object that has a north pole has a
south pole
Magnetism
Magnetic Field

Region around a moving charged
particle through which a force is
exerted on another moving charged
particle

Similar to Electric Fields
Magnetic Field Lines




Lines are not real
North  South (outside magnet)
Can not cross
Closer lines mean stronger field
Magnetic Field Lines
Magnetic Field Lines
Magnetic Field

Magnetic Field is a region around a
moving charged object through which
a force is exerted on another moving
charged particle

Motion of particle must be perpendicular to the
magnetic field
Magnetic Fields

Magnetic Fields are often illustrated
using arrows
Magnetic Fields

What about into the page or out of the
page?
Into Page
Out of Page
Magnetic Hand Rules

To determine the direction of the force,
we use hand rules.

Different hands for different charges


Right hand for Positive charges
Left hand for Negative charges
Conventional Current

Conventional Current follows the old
“convention” that positive charges are
the charges that are moving in current

Use Right Hand Rule
Electron Current

Electron Current is the reality that
negative charges are the charges that
are moving in current

Use Left Hand Rule
Magnetic Hand Rules

Point index finger in direction of motion

Point palm or other fingers in direction
of magnetic field

Point thumb in direction of Magnetic
Force
Example

An electron is moving through a
magnetic field as shown below. In
what direction will the magnetic force
be?
e

Out of page
Another Example

An electron is moving through a
magnetic field as shown below. In
what direction will the magnetic force
be?
e

Down
Force on Wire

Still use hand rule to determine the
direction of the magnetic force

Index finger is the direction of the
current
Magnetic Fields produced by
Currents

A current carrying wire also produces
a magnetic field

Direction follows second Hand Rule
Magnetic Fields produced by
Currents




Second Hand Rule
Thumb in direction of current
Curl fingers around wire
Curled fingers show direction of
magnetic field
Example

What is the direction of the magnetic
force exerted on wire 2 by the
magnetic field produced by wire 1?
I-
1
2
IDown
Example

What is the direction of the magnetic
force exerted on wire 1 by the
magnetic field produced by wire 2?
I-
1
2
Down
I-
Magnetic Fields produced by
current carrying loops



Imagine current flowing through the
loop below
In what direction will the magnetic field
be produced inside the loop?
Into Page
I-
Electromagnets

Temporary magnet caused by an
induced magnetic field from current
carrying wires.
Electromagnets


Current carrying wire produces a
magnetic field
Coiling the wire bunches up the
magnetic field inside the coil
Electromagnets

Increasing the strength of the
electromagnet:



Increase Current in wire
Increase number of coils
Add an iron core
Electromagnetic Induction

If charged particle moving through a
magnetic field feels a force, shouldn’t a
moving magnetic field exert a force on
a charged particle?
Electromagnetic Induction

A voltage can be “induced” in a wire by
moving a magnet near the wire.


often a coil of wire is used
Faraday’s Law

Induced voltage is directly proportional to
the number of coils, cross-sectional area
of the coils, and rate of change of
magnetic field
Electromagnetic Induction
Electromagnetic Induction
Electromagnetic Induction

Inducing a current in a coil of wire
creates its own magnetic field
Electromagnetic Induction

Changing direction of magnetic field
changes direction of induced voltage

Creating an alternating current (AC)

Alternating Current

Current alternates direction at a regular
rate


Electrical Outlets
Direct Current

Current flows in one direction only


Batteries
Sim
Generators & Motors

Device to convert between Electrical
and Mechanical Energy

Generator


Converts Mechanical Energy to Electrical
Energy
Motor

Converts Electrical energy to Mechanical
Energy
Generator
Motor