Some Final Questions on Magnetism

So, because of my test on magnetism tomorrow ( D: ),  I have a list of questions about magnetism that came up as I was going over the concepts again. Here they are in case anyone had these questions/just to help me clarify them to myself.


Question 1: What is the angle of declination and the angle of inclination?

Answer: The angle of declination is the angle between true north or geographic north, and magnetic north. Depending on where you are on the Earth, this angle can differ a lot. For example, one not-very-recent statistic states that Eureka, NWT, has an angle of declination of 98 degrees (the magnetic north pole is at 98 degrees to true north there). On the other hand, Churchill, Manitoba, has an angle of declination of 0 degrees, meaning at Churchill magnetic north and true north are in line with each other. To be honest, I'm not too sure how this works.
             The angle of inclination is the angle between the surface of the Earth and the Earth's magnetic field. At the equator, the magnetic field is parallel to the Earth's surface, but near the poles the magnetosphere :) is at a steep angle to the Earth's surface. Right at the poles, the magnetic field and the Earth's surface are perpendicular to each other. Angle of inclination is measured through a dip needle.


Question 2: What is domain theory?

Answer: Domain theory is a theory that explains certain properties of ferromagnets (materials that magnetize extremely well). The theory states that ferromagnets have inside them tiny regions of atoms that are all oriented the same way, so that they have a north and south pole. Generally, these domains are all oriented randomly to each other, so they have a net magnetic effect of zero. However, with a strong enough external magnetic field (such as a coil with current flowing through it), these domains can be aligned to give us one overall north and south pole. If the magnetic field is increased, the domains will become more aligned. There is a point, though, when the domains cannot be aligned any further. Logically, this makes sense.


Question 3: What does domain theory prove?

Answer: Domain theory conveniently explains...

• why ferromagnets can become magnetized after stroking with another magnet (a big example of this would be ships and buildings becoming magnetized during construction as a result of the Earth's magnetic field)
• why a broken magnet becomes two smaller magnets, not just a north pole and a south pole
• why a strong magnetic field in the opposite direction can switch the poles of a magnet

It also explains how magnetic properties can be lost through heating or dropping a magnet: this jostles the orientation of the domains enough that they resume their random orientation.

For a more in-depth look at domain theory, among other things, go here: Magnets, Magnetism and the Magnetic Field


I actually had some other questions too...but I don't know all their answers.

Unanswered question 1: Is there any difference between magnetic lines of force and magnetic field lines?

Unanswered question 2: If we say that the magnetic fields were cancelled out, does that mean there isn't any field there anymore?

If I find the answers, I will try to blog them. :)