Chapter 28 Magnetic Fields

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18 Οκτ 2013 (πριν από 3 χρόνια και 10 μήνες)

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Chapter
28



Magnetic Fields

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Reading Assignment

Only Through Section 6


End of Chapter Problems (Online Homework)


Prior Knowledge


Vocabulary

Magnet

Pole

Ferromagnetism

Magnetic Field

Compass

Lodestone

Declination



Equations

None

























28.0


Intr
oduction

28.0.1

What are the two poles of a magnet called?


North & south


28.0.2

Read Carefully, what does the introduction say about the Earth’s Magnetic field, (is this
surprising)?


Scientists cannot say for certain the REASON for earth’s magnetic fiel
d and why it
switches poles once in a while (millions of years)



28.1


Magnetic Fundamentals

28.1.1

How do magnetic poles attract and repel? (Does north attract north or south, what about vice
versa…)



Opposites attract; like repel


28.1.2

What is the
strongest and most frequently found type of magnetism?


Ferromagnetism (iron
-
like)


28.1.3

Can a magnet stick to a surface that isn’t magnetic…why? Can a magnet stick to any
surface…why?


No. It must “induce” (create) a magnetic field from the door’s surf
ace. Only surfaces made
of ferromagnetic materials.


28.1.4

What happens if you chop a magnet in half? Can you separate magnetic poles?




No. It doesn’t have to be in “half” either. Each END created will

be a new pole.








28.2


Magnetic Fields

28.2
.1

We use the symbol
E

to symbolize electric field, what symbol do we use for magnetic field?


B


28.2.2

What unit do we measure magnetic field in?


Tesla (also Gauss)


28.2.3

Electric field starts at the positive charge and


ends at the negative charge,
what about

magnetic field (which pole does it

start and end at)?



North and goes south (N






㈸⸲⸴

Can I draw a magnetic field line, or only magnetic field loops?


Loops (the closer together, the stronger)



28.2.5

Take a guess…how does the magneti
c field of an object (and the magnetic force) change with
distance (think about electric fields)?


Inversere square (decreases)



28.3


Physics at Work: Lodestones

28.3.1

What is a lodestone?



A naturally magnetic rock that retains it’s magnetic field

f
or a long time


28.3.2

Why might you think that lodestones are important historically?

The helped Columbus find America!





28.4


The Earth and Magnetic Fields












28.4.1

Give a continent (geographically) that might be the center of the Earth’s n
orth magnetic pole.


Antarctica


28.4.2

What is the approximate strength of the Earth’s magnetic field?


5 x 10
-
5

T


28.4.3

Is the Earth’s magnetic field a constant? What is happening with it?


No. It’s decreasing.



28.5


Physics at Work: Compasses and

the Earth

28.5.1

Explain what a compass is?


A magnetic direction
-
finding & location device


28.5.2

What is declination?

The difference in angles between north & magnetic south poles


28.5.3

How could you measure latitude with a free standing compass?


See how far downward the needle points.



28.6


Ferromagnetism

28.6.1

What is magnetic domain?


A magnetic domain is a

small section

of a ferromagnetic material in which the atoms in this
section are magnetically aligned. Adjoining domains will tend to be

aligned magnetically in
the same way if the material is magnetized, but this tendency does not exist for domains in
samples that are not magnetized.


28.6.2

Why are most materials non
-
magnetic?


The
spins in the electrons are balanced with other electrons

spinning the opposite way; or,
the material is warm enough that atoms move around too much to ever align magnetically.


28.6.3

What happens when a ferromagnetic material is subjected to an external magnetic field?


The individual domains tend to align wit
h that field.


28.6.4

Why doesn’t an un
-
magnetized ferromagnetic material (like iron) go back to this un
-
magn
e
t
i
zed
state after being subjected to an external magnetic field?


It does tend to go back depending on the amount of exposure time within the fiel
d and the
strength of the field.




28.23
-

Gotchas

Try to create three multiple choice questions (remember, if they’re really good you could see
them on a test!)




















28.24
-

Summary

Add some of your own notes to the summary. (Don’t just co
py the summary word for word!)