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.  

The Past Two Weeks of Class!

When we started classes we were asked to build a simple electric motor. It was a challenge for us because we had barely studied electricity, and we had to find the motor we wanted to build, the necessary informations for building it, and buy all the materials. At first I built the "plastic cup motor" that you can see in the video in the link at right;  http://www.youtube.com/watch?v=ziWUmIUcR2k. This video is a very good source of information, because it is detailed, and clear; however it is not easy to built the motor as it looks in the video. I only could find a wire that was too heavy, so it would not spin when arranged as a coil, also the alligator cable clips wouldn't connect to the battery as it is shown in the video. Another problem that I could identify in the video is that it does not says how potent your magnets should be, because if you use weak magnets, as I did, the coil will not spin either. As a consequence of all those factors my plastic cup simple electric motor didn't work.

After building our motors we were asked to bring them to class so that we could show to our colleges and exchange ideas. My college showed me a simpler motor that I could easily built, and would not need to buy additional materials. So I built the motor, and was relieved that it worked. You can see how to built this simple motor in the pictures bellow, they are not accurate, but with them you can have an idea of how this motor works.

You can see all the materials that are need to built this motor.

You can see how to arrange the materials so that the motor can work.

You can see what happens when the motor is working.

After managing to build a simple electric motor we were split into groups, and each group was given a topic so that we could understand why our motor worked or did not. My group was given the topic; transferring chargers. We did a poster with drawings explaining our topic, and after presented briefly to the class. We explained that there are three ways in which chargers can be transferred; charging by friction, charging by conduction, and charging by induction. Charging by friction is the transfer of electrons from one uncharged object to another by rubbing. For example if you are walking in a carpet with your socks on and you rub them in the carpet, electrons will move from the carpet to your socks causing an overall negative charge on them. Charging by conduction is the transfer of electrons from a charged object to another object by direct contact. For instance when your socks that are now negatively charged touch your skin the electrons present in it will be distributed throughout your body. Charging by induction is the movement of electrons to one part of an object that is caused by a electric field of a second object. For example when you touch a doorknob after walking in a carpet with your socks on your fingertip produces an electric field that repels the electrons in the surface of the doorknob, and will move away from your finger. This movement will produce an induced positive charge on the doorknob.

After all groups presented we were expected to achieve eight learning goals that were stated like this;

1. I can explain how electrical charges interact.

2. I can give examples of how charges can be transferred between materials and explain them.

3. I can explain how an electric current is produced.

4. I can compare conductors with insulators.

5. I can explain how resistance affects current.

6. I can use Ohm's law to compare resistance, current or voltage.

7. I can built series and parallel circuits and describe them.

8. I can explain the relationship between power, voltage and current.
I still can't understand why my simple electric motor worked. I know that a circuit was created between the battery and nail, and that the voltage in the battery caused a current. The wire was made of copper which is a conductor so that charges could flow. The charges in the wire went to the nail, that was also a conductor because it was made of metal, and at last they went to the magnet. I don't know about the magnet's role, but I can deduce that it was the responsible for making the nail spin. I am not sure why the nail spun after that, I think that it has something to do with the chargers being in contact with the magnet, and their electric field interacting with the magnet's magnetic field.
Did I achieve the eight learning goals?
1. I can easily explain how chargers interact. Positive chargers repel each other, negative chargers also repel each other, and positive and negative chargers attract each other. Summarizing; chargers that are the same repel each other, while chargers that are different attract each other.

2. I can give examples of how charges can be transferred between materials and explain them as I just did in the third paragraph where I explain the topic that my group was given.
3. An electric current is the continuos flow of charges through a material, but it requires an electric circuit to be be produced. An electric circuit is a complete, unbroken path through which chargers can flow. Imagine you have a circular race track, and cars are moving continuously through it. They make many turns, and keep moving through the race track. The move of cars is equivalent to current. If the race track was broken the cars would not be able to move, it provides that the cars are able to move continuously. The race track is equivalent to a circuit.
4. A conductor is a material through which chargers can flow easily. Atoms contain electrons that are bound loosely in a conductor. Conductors have less resistance, consequently charges will always choose the path of a conductor, because they always choose the path of least resistance. Because of that conductors are often used to carry electric charges. An insulator is material through which charges cannot flow easily. The electrons are bound tightly to their atoms and do not move easily in an insulator. Insulators have more resistance, so chargers will never choose the path of a insulator, because they always choose the path of least resistance. Because of that insulators are often used to stop the flow of charges.

5. Current depends on voltage and resistance. Voltage is like a push for the flow of electrons start. It requires a source of energy, a battery, to maintain itself. Resistance is the measure of how difficult it is for charges flow through a material. As resistance increases in a circuit, the current's speed decreases. The greater the resistance, the less current there is for a given voltage.
6. Ohm's law says that the resistance is equal to the voltage divided by the current.

7. If all the parts of an electric circuit are connected one after another along one path, the circuit is called a series circuit. In a series circuit, there is only one path for the current to take. If a light bulb burns out in a series circuit the circuit will be broke and there is no other path for the current to take. So if one light bulb burns out, the others won't have their lights going on as well. The light bulbs in a series circuit becomes dimmer as more bulbs are added, because the resistance increases and the current decreases as there is just one path to take. In a parallel circuit, the different parts of the circuit are on separate branches. In a parallel circuit, there are several paths for current to take. If a light bulb burns out in a parallel circuit the circuit will not be broken, because charges will still be able to move through the other branches. One light burning out does not affect the other lights, as there are more paths in which current can take. If you add a light bulb in a parallel circuit the brightness of the other lights in the other branches will not be affected, but the battery will run out faster.

8. The rate at which energy is transformed from one form to another is known as power. The unit of power is the watt (W). You can calculate power by multiplying voltage by current.

Power= Voltage x Current

P= VI

Using Google Docs we had to create a multiple choice quiz of 10 questions applying all the concept of those topics. The quiz could not include formulas and definitions, and as you can see I posted on my blog so that everyone can have a chance to do it. Some of the topics that I couldn't quite understand at first were 7 the one about series and parallel circuits and 6 the one about Ohm's law. If you are having trouble to understand series and parallel circuits you can click on this link;http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc. If you click on the link, and in the website click "Run Now!" you will be able to built parallel and series circuits and see how they work. It helped me a lot, and now I can finally understand them. To understand Ohm's law I just needed to review carefully my book, and after some minutes I could get it.

My goals for this semester are; putting my best effort, and managing my time well. Managing my time well is my most important goal, because last Semester I didn't do it so, and eded with late works, and little time to study. I will a try to be more organized in this semester, and hope that in consequence I will achieve better grades, and will end 9th grade without doubts.

Check out my Electricity Quiz!

https://docs.google.com/spreadsheet/viewform?formkey=dFRtU1hNTlhQRkpFRVpmVUVVaTZoVmc6MQ