6 - Unit 4, Section 2

Electric and Magnetic Forces and Fields

Unit 4, Section 2

VOCABULARY

• Ion

• Static Charge

• Electric Force

• Electric Field

• Insulator

• Conductor

• Electric Discharge

• Magnetic Field

• Magnetic Domain

ELECTRONS IN
SOLIDS

• Electrons aren’t

“stuck” to one
nucleus in a solid

• They can move from

one nucleus to
another

• Physical motion or

contact can cause
electrons to “jump”
from one solid to
another

WHAT HAPPENS WHEN ELECTRONS
JUMP?

•A balloon is rubbed on your hair

–The electrons in your hair are held more loosely than the

electrons on the balloon

•Which way do the electrons jump?

–What happens to the overall charge of your hair?

–What happens to the overall charge of the balloon?

STATIC CHARGE

An imbalance in the electric
charge of an object

Caused by the transfer of
electrons from one object to
another

Can you have a positive
material without a negative
material?

ELECTRIC FORCES

•What keeps the electrons from flying off of the nucleus?

– The positive nucleus and the negative electrons are attracted to

each other

•Electric Forces – the force that all charged objects exert (place)
on each other

TYPES OF ELECTRIC FORCES

+

+

-

-

Like Charges REPEL
+

-

Opposite Charges

ATTRACT

MORE ABOUT ELECTRIC
FORCES

•The electric force between two
objects becomes stronger as:

–They get closer

–The electric charge on them

increases

ELECTRIC FIELDS

•Do objects that are
charged have to touch each
other to exert a force?

•A charged object exerts an
electric field around itself

•Just like electric forces,
electric fields get stronger
as you get closer to the
object

CONDUCTORS AND INSULATORS

•Conductor – A material that contains electrons that can move
easily through the material

–Metals – the best conductors

•Insulator – A material that contains electrons that cannot move
easily through the material

–Nonmetals – the best insulators

ELECTRIC DISCHARGE

•Electric Discharge – the rapid
movement of excess charge from one
place to another

–Lightning – a natural example

–So is shocking yourself on a

doorknob

–But how?

GROUNDING

•Grounding – the process of
providing a pathway to drain excess
charge

–Usually with a wire or pipe

•Charge flows through the grounding
pathway and not through anything else

–Used to protect buildings, people

The First Magnets

•Magnetite – a naturally-occurring mineral

•It attracts others pieces of magnetite and
iron

•If a piece of iron was rubbed with
magnetite, it acted like magnetite

Compasses

•Sailors found out that, if you
rubbed an iron needle on
magnetite and placed it on the
surface of water, it pointed
north

•These were likely the first
compasses
•But why did they point north?

•And how do magnets work?

Magnets

Magnet – a piece of magnetite, iron, or steel that attracts other
objects made of iron or steel

Magnets can attract things like nails, paper clips, etc.

Magnets can also attract or repel other magnets

Magnetic Poles

WHY DO

MAGNETS

WORK?

There’s just one
question, though…

How Do Magnets Work? An Observation

•Play around with the magnetite a little

•Hold two pieces close together. Notice how they either:

•Repel each other

•Attract each other

•It appears that magnets affect each other at a distance

•What did we say caused electric charges to affect each other at a
distance?

Magnetic Fields

•The force exerted through a magnet, that
affects iron or other magnets at a distance

•The field bends and connects the two
poles

•The field is in all three dimensions, not just
on a flat surface

•The closer the lines are, the stronger the
field is in that area

HOW MAGNETIC FIELDS ATTRACT

AND REPEL

Okay…But What Creates Magnetic Fields?

•First, let’s think about how Earth moves around the Sun

•Earth is moving two ways

•It is orbiting the sun

•It is rotating on its own axis

•Is there something we’ve talked about, that’s sort of like Earth
moving around the Sun?

The Atom!

+

-

Nucleus

Electron

•The electron is orbiting
around its nucleus

•It’s also rotating around
its own axis

•Each electron produces
its own magnetic field

•Each atom becomes a
tiny magnet

Magnetic
Domain

•In iron, each atom’s magnetic field can point
in the same direction

•All of those fields add up to one larger field

•The iron becomes magnetic

•Magnetic Domain – A group of atoms with
all of the magnetic fields pointing in the
same direction

Finally, A Definition For “Magnet”

Magnets and iron have small magnetic domains, each with
their own magnetic fields

Those domains line up and produce one big field, which
makes the material magnetic

In magnets, this field is permanent

In iron, it is temporary

Wait…Birds?!

•Some animals, like birds, bees
and trout, have tiny pieces of
magnetite in their bodies

•They can be used to detect
Earth’s magnetic field

•This helps them determine
direction and navigate