Wednesday, April 25, 2012

Electricity and Magnetism Unit

The unit that we just finished learning is the interaction between electricity and magnetism. We had different topics, and various goals that we were supposed to complete to make sure we had learned what we were supposed to. The goals that we have to be able to explain are the ones from EM9 - EM 21. I will be addressing what I know about each topic.

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

The properties of a magnet :
-Usually made of metal
-Material that attracts iron and material that contain iron.
-A good conductor
-Is hard and solid
-All magnets have an end pointing north and one pointing south, called magetic pole
-The magnetic effect of a magnet is strongest at the poles
-It is surrounded by a magnetc field
-It has an attraction or repulsion between magnets, a magnetic force.

The interaction of metals are really similar to the interaction between electrical charges.

As you can see in the picture the poles that are alike repel each other, however; poles that are unlike each other attracts one another.

The reason why they react when getting closer is because of the magnetic field around them. The magnetic field enables the magnets to interact without even touching each other. 

The magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole. 

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

A magnetic domain is a grouping of atoms that have their magnetic fields aligned. But what is an atom? An atom is a particle that is composed of neutrons and protons in the nucleus and electrons surrounding it. 
  • The entire domain acts like a bar magnet wih a north pole and a south pole.
Domains are alligned differently in magnetized iron and unmagnetized iron.
  • Unmagnetized iron 
 In an unmagnetized iron the domains point all to different directions. These arrows represents the force of the domains, it shows in what direction the force of the domain is working on.
  • Magnetized iron
In a magnetized iron all or most of the domains point to the same direction. The magnetic field of the domains are aligned, all the domains puts their force to the same direction.

Strong magnets are the ones with its domain aligned. The materials that show this property are known as ferromagnetic material. Iron, nickel and others are examples of ferromagnet material.  

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

Electromagnetism is the relationship between electricity and magnetism, the relationship between them is the electric current producing a magnetic field.
As you can see in the picture, the picture of the left, the compasses points north because it aligns itself with the earth's magnetic field. However; that only happens when there isn't any other current around it. Because when an object with a current, for example a wire, is present the compass needles will align itself with the magnetic field from the current of the wire.  

The magnetic field produced by a current has three characteristics,
- The field can be turned on and off
To do so, you simply turn the current on or off. An example is the light. You have the switcher to turn the light on or off. 
-It can have it's direction reversed 
You can change the direction of the magnetic field by reversing the direction of the current. Because when current reverses the magnetic field also reverses. 
-It can have it's strength changed
If the number of turns, loops, or coils increases you can increase the strength of the magnetic field. A coil of wire with a current is called a solenoid. 

EM12. I can outline the difference between DC/AC current and its uses

For you to understand the difference between the two types of current, you have to know what is to induce an electric current. An electric current is induced in a conductor when the conductor moves through a magnetic field. Generating an electric current through the motion of a conductor through a magnetic field is called electromagnetic induction.

To induce a current in a conductor, either the conductor can move through the magnetic field or the magnetic itself can move.

Direct Current -
In an induced current, charges can flow in one direction only or alternate the directions. A current in which charges flow in only one direction is called direct current, in a simple way, DC. A direct current can be induced from a changing magnetic field or produced from an energy source like a battery. In the battery the charges will flow from one side to the other, until both sides are balanced.
Alterning Current -

The alterning current is all explained in its name! The current keeps alterning its direction repeatedly. It consists of charges moving back and forth in a circuit.
Alterning current has a greater advantage over direct current because it's voltage can be easily raised or lowered to a higher or lower voltage. Which means that electrical energy can be sent from a long distance in a high speed, but be reduced to a safer level when getting to the right point, which can be safer.


EM13. I can explain why the Earth behaves like a magnet and the consequences of it.

Why does a compass always points north when no current is around it? The answer to this question is because the earth has its magnetic field surrounding its poles. The Earth is similar to a magnet. It has two poles, and a magnetic field surrounding its poles. Because the Earth works like a magnet, the compass' needle points north because it aligns itself with the Earth's magnetic field.
Earth's magnetic field extends into space, where is a place full of electricalle charged particles. Earth's magnetic field affects the movements of electrically charged particles in space. Earth experiences a solar wind, which is a stream of electrically charfed particles flowing at high speed from the sun. The solar wind pushes against Earth's magnetic field, and the region which it is shaped is magnetosphere.

EM14. I can explain the importance of grounding wires and using fuses/circuit breakers.

When we have contact with a wire with a current we can be shocked, it might hurt a little but it can even be fatal. So for people's safety grounding wires and circuit breakers were created.
Sometimes the electric charge can flow through the person rather than through the wire. It is considered a short circuit between the wire and the person. A short circuit is a connection that allows current to take the path of least resistance.
We always need to know that there is a difference between the electrical discharge that you feel from the carpet and an electrical discharge from touching a high-voltage wire.
The Grounding is a really important role in electrical safety. One way to protect people from electric shock and other electrical danger is to provide an alternate path for electrical current.
A circuit is electrically grounded when charges are able to flow directly from the circuit into Earth in the event of a short circuit.
A method of grounding is to use a third prong on a plug, like the image below.

The third prong which is round, connects any metal pieces of the appliance to the ground wire of the building. If a short circuit occurs in the appliance, the electric charge will flow directly into Earth. So anyone who touches it will be safe.

The Breaking Circuit are used to break circuits that are overloaded and can result in danger. In order to prevent circuits from overheating,  fuses and circuits breakers are added to circuits.
A fuse is a device that contains a thin strip of metal that will melt if there is too much current through it. If the metal melts or blows it breaks the circuit. If the circuit is broken, the current stops. Which prevents danger.
However; a disadvantage of a fuse is that, once it is burned it has to be replaced. To avoid having to replace it, there is a new device called circuit breakers. A circuit breaker is a reusable safety switch that breaks the circuit when the current gets too high.

EM15. I can explain how an electromagnet works and cite applications for them.

Your life will be much easier if you know what is a ferromagnet and a solenoid before learning how an electromagnet works. A ferromagnetic is a material of iron that has a strong characteristics of metal. A solenoid is a coil of wire with a current. 
So, now that you know what is a ferromagnet and a solenoid i will explain what is an electromagnet and how it works. An electromagnet is a solenoid with a ferromagnetic core. The magnetic field of an electromagnet is produced by the current in the wire and the magnetized core. An electromagnet is a strong magnet that can be turned on and off. 

EM16. I can explain how a simple motor works (parts and function).

Moving an object over a distance is called energy. When the energy interacts with eletric current it is called electrical energy, and when an object has an energy that it is able to move it is called mechanical energy.
Energy can be transeformed from one form into another. When a wire with a current is placed in a magnetic field, electrical energy is transformed into mechanical energy. It happens when the magnetic field current causes the wire, or another conductor to move.

To transform the electrical energy to mechanical energy we usually use a device called an electric motor.

This image represents an electric motor. The yellow circle is called a commutator.
A commutator is a ring split in half, in which each half is attached to one of the armature which are the two wires coming out of the commutator. 
The wires that come out from the commutator is called armature. The armature is the wire that connects with the commutator and is also the object that will turn continuously.
The huge blue object around the armature is the permanent magnet. The permanent magnet will always be around the armature to keep the magnetic field around the motor.
The commutator is connected by the white lines coming from the green baterry. In the end of each white line has an object called brush, that touches the commutator. Though we can't really see it in this picture.

The function of each part of the motor :
-Brushes: The brushes conduct current to the armature.
-Armature: The armature is attracked by the magnetic field and it alligns itself correctly with the magnetic field, moving up or down.  
-Commutator: The commutatot rotates with the armature. It repeadetly reverses the flow of current through the armature.

How the motor works? 
For a motor to work, you have to make the armature spin continuously. When the energy source pass by the brushes to the commutator, the current flows in one direction to the armature. But because of the magnetic field that is created by the permanent magnet, the current has to align itself with the magnet, as a result the armature turns to a vertical position. However, the current keeps reversing it's direction, which makes the armature spin continuously. 
This is an image showing how the motor works:

EM17. I can describe how a generator and a transformer work.

A generator, opposite from the motor, uses motion in a magnetic field to produce an electric current. It transforms mechanical energy into electrical energy. But to understand how a generator works you have to know what is an electromagnetic induction and the types of current, (the types of current we already saw in EM.12, if you forgot go review it!) 

An electric current is induced in a conductor when the conductor moves through a magnetic field. To th generate an electric current from the motion of a conductor through a magnetic field is called electromagnetic induction. That is to say, when you use the motion, the movement of a conductor and as a result electric current is produced. 
To induce a current in a conductor, either the conductor or the magnet can move through the magnetic field. 

The picture in the upper side you can notice that the coil is moving up when the south pole is near the conductor, and besides it the coil is moving down when the north pole gets near the conductor. A current is induced in a coil of wire when the coil moves in a magnetic field. And the opposite occurs in the picture below. A current is induced in a wire when a magnet moves through a coil of wire. 

As you can see in the picture the parts of a generator and parts of the motor are really alike, there is only
 one difference, which is the crank. 

This is a simple AC generator. As the crank is turned, the armature rotates in the magnetic field. One side of the armature moves up and the other moves down. This motion induces a current in the wire. After the armature turns halfway, each side of it reverses direction in the magnetic field. The side that moved up moves down, and vice versa. AS the armature turns, slip rings turn with it. The slip rings my remind you of the commutator in a motor. As they turn, they make contact with the brushes. The brushes are connected to the rest of the circuit, in which the generator becomes an energy source. 

The crank is used to rotate the armature, and the slip ring is really similar to the commutator from the motor. 

EM18. I can explain the importance of transformers to power grids.

A transformer is a device that increases or decreases voltage. A transformer consists of two separate coils of insulated wire wrapped around an iron core. 
The primary coil, the first coil, is connected to a circuit with a voltage source and alterning current. The other coil, the secondary coil, is connected to a separate circuit that does not contain a voltage source. 

There are 2 types of transformers, the step-up or step-down transformer. The step-up transformer has less coil around the primary coil and more in the secondary coild so that it can increase the voltage. 
There are more loops in the secondary coil, therefore; it increases the voltage. In the other hand, the step-down transformers do the opposite as the step-up transformer. As you predicted the step-down transformer decreases the voltage, having more loops in the primary loops than in the secondary loop, like this:
Transformers are really important because they can be efficiently used in transmissions of electrical energy. For example, to transmit electrical energy from long distances, the best way is to transmit it in high voltage, but when getting to the place where the energy will be used, the transformer can decrease the energy for our safety. 

EM19. I can explain methods of power production and distribution.

There are a lot of different methods of power production and distribution, here are some of them. 
-Fossil Fuels
-Nuclear Energy
-Hydroeletric Energy
-Solar Energy
-Wind Energy
-Geothermal Energy

I will explain one of the examples which is Solar Energy. The conversion that happens is from kinetic electromagnetic to kinetic electrical energy. 
The solar energy like its name, gets the energy from the sun to produce energy. 

Some advantages of the solar energy are:
-It is renewable
-It is a clean transformation 
Some Disadvantages of the solar energy are:
-It is only possible when sun is present, so mostly during the day. But days that are cloudy is difficult. 
-It is also really expensive, which makes harder for people to use this type of energy. 

EM20. I can describe the differences of 110v/220v and main advantages and disadvantages of each.

The difference between 110v and 220v is that 220v is stronger and more efficient.

Some reasons why 220v is better, is because you lose less energy, it is cheaper, stronger and more efficient.  Since it is high voltage during the transmission of energy, it generates less heat and therefore loses less energy. Also, the wires for 220v are thinner, so it is a lot more cheaper than 110v. But a disadvantage is that it is more dangerous, if you get shocked it will have a greater impact than 110v. 

The advantage of 110v is that, it is safer. There isn't enough voltage to use a path to the ground, so it's a lot harder to get shocked. Some disadvantages are that it is expensive plus it's weaker than 220v. 

 Here in Brazil we use both 110v and 220v because when they started installing this a long time ago they didn't plan and were influenced by both the European (110v) and American (220v) system and installed both and to change it now, would be really expensive. We need 220v because some of the electric objects need more power to work, like the freezer. But simple electronic materials like computers can be used in 110v. 

EM21. I can describe the advantages and disadvantages of electrical energy.

Electrical energy is the presence and flow of an electric charge through a conductor. 
Some advantages of it are:
-It is clean
-It's fast
-It's efficient
-It's easy to distribute in different places
Therefore, many people use electrical energy. But, the way we get the energy is a disadvantage. It polutes the environment and it is unsafe.