Download Reading Guide CH 28KEYJWW

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 – Introduction
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 field 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?
surface…why?
Can a magnet stick to any
No. It must “induce” (create) a magnetic field from the door’s surface. 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  S)
28.2.4
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 magnetic 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
for 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 north 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 with that field.
28.6.4
Why doesn’t an un-magnetized ferromagnetic material (like iron) go back to this un-magnetized
state after being subjected to an external magnetic field?
It does tend to go back depending on the amount of exposure time within the field 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 copy the summary word for word!)