Learning Goals 9-21

Electricity and Magnetism Unit 

We are almost ending the year, and it is expected that we have learned all learning goals from the electricity and magnetism unit. We spent the whole semester on it; we learned what are magnets, what is electricity and how do they interact. In this post I will explain what is addressed in each topic from 9 to 21, based on my understanding in electricity and magnetism. 

EM9. I can describe the properties and interactions of magnets.

A magnet is a material that produces a magnetic field. A magnetic field is the area of magnetic force around a magnet mapped by invisible lines. The magnetic field is the responsible force for pulling on ferromagnetic materials, and attracting and repealing other magnets. 

Because of the magnetic field magnets attract ferromagnetic materials, such as iron, repel or attract other magnets, and when allowed to swing freely have one part that will always point North. 

Magnets are divided between two poles; North and South. Unlike poles attract and like poles repel. A North pole will always attract a South pole, and will always repel a North pole. A South pole will always attract a North pole, and will always repel a South pole.

One part of a magnet will always point North when allowed to swing freely. This happens because Earth has also a magnetic field, and when a magnet is allowed to swing freely its magnetic field aligns itself with Earth's magnetic field. However the part of the magnet that will point North won't be the North pole, but yes the South pole. Earth's magnetic poles don't mach Earth's geographic poles, they are close with a tilt of 11 degrees. Earth's magnetic poles move around, and sometimes even flip. We cannot determinate the time that the magnetic poles reverse, but we know that they did many times in the past by looking to magnetic rocks that lie along sea floor. Because of them we can tell that Earth's magnetic field is reversed, as a result of that we have the Southern polarity close to geographic North and the Northern polarity close to geographic South. So whenever a magnet is allow to swing freely its South pole will point to the North magnetic pole until Earth's magnetic poles reverse again.

EM10. I can describe how the magnetic domains are arranged in a magnetic/non-magnetic material.

The magnetic properties of a material depend on the structure of its atoms. On the nucleus of a atom, its center region, two material can be found; neutrons, which carry no charges, and protons, which carry positive chargers. Outside the nucleus electrons can be found, which carry negative charges. Every electron has a property called electron spin, so it behaves as if it were spinning. Spinning electrons produce magnetic fields. When electrons form pairs that spin in opposite directions the magnetic fields are canceled. Atoms that contain electrons that had its magnetic field canceled have weak magnetic properties. However in some atoms there are electrons that didn't form pairs and because of that didn't have their magnetic fields canceled. In these atoms we can find strong magnetic properties. 

Most materials have the magnetic field of its atoms pointing in random directions, in consequence the magnetic fields cancel one another almost entirely. The magnetic force is so weak that you cannot even detect it. Although in some materials the magnetic fields of many atoms are aligned with one another. A group of atoms that have their magnetic fields aligned is called a magnetic domain. Magnetic domains act as bar magnets having two pole; North and South. The direction in which they point determines if the material is magnetized or not. A magnetized material have all or almost all domains pointing at the same direction, so that the fields are aligned. A non magnetized material has its domains pointing at random direction, what results in some domains canceling the magnetic fields of other domains. 

EM11. I can explain the connection between electricity and magnetism (electromagnetism).

An electric current produces a magnetic field, so whenever there is electricity there is magnetism. But how do we know that? If you place some compasses needles at the floor you will see that they all point at the same direction; North. That happens because the compasses needles aligned themselves with Earth's magnetic field. If you connect an electric current to the needles you will see that that they all will point at different directions, because they will align themselves with the magnetic field generated by the electric current. That is how we know that when you have an electric current you also have an electric current. 

EM 12. I can outline the differences between DC/AC current and its uses.

An electric current is the continuous flow of charges through a material. A current that consist of charges flowing in one direction is called direct current, DC. A DC is usually produced from an energy source such as a battery. A battery is placed in a circuit and what happens is that charges flow away from one end of the battery going to the other way of the battery. When you have a magnet and a conductor, and you move one of them a current is induced. In this current charges move back and froth because of the movement of the magnet or the conductor. The alternating movement of charges create a alternating current, AC. 

EM 13. I can explain why the Earth behaves like a magnet and the consequences of it.

The English physician Sir William Gilbert made experiences with compasses and confirmed that a compass always points to the same direction. He concluded that this happens because Earth behaves as a giant magnet. Earth has a magnet field surrounding it and two magnetic poles, just like a bar magnet. However Earth's center doesn't contain magnetic rock because the temperature is too high to have a magnet material. Earth's magnetism is still a mystery. Earth has magnetic poles, they are located where the magnetic force is stronger and are not in the same place of geographic poles. Ferromagnetic material can be made into magnets by a strong magnetic field, therefore Earth can magnets out of ferromagnetic materials.