Unit 7 Reflection

This unit, we began learning about magnetism first. The source of magnetism is moving charges. The charges (electrons) are spinning randomly when not magnetized. Domains, however, are clusters of electrons all spinning in the same direction. Magnetism gives them a net direction. This happens when a magnet is brought near a cluster of randomly spinning electrons. In order for the direction to stay the

same, and because the magnet is much stronger than the cluster of electrons, the electrons are all forced to align so that the magnetic field can continue to flow. In an electron flied, there are two poles. The North and south pole. The magnetic field runs out of north pole, and then to the south.

The reason the charges are forced to move this way in a magnetic field is because: like poles repel and opposite poles attract. When the electrons leave the north pole, they are attracted to the opposite pole (the north pole) that they were just repelling. 

There were three big questions asked this unit:

How do you turn a paper clip into a magnet?

The Domains in a paper clip are random, and a magnet had a magnetic field. When the magnet is close to the paperclip, the domains align to match the magnetic field of the magnet. The paperclip now has a North and South pole. The North pole of the paper clip is attracted to the South pole of the magnet, and thus the paperclip sticks to the magnet

Are cosmic rays harmful or helpful, considering the Earth's magnetic field?

The cosmic rays are helpful because there is a field around the earth, and when a charge enters the field, it circles around the file lines, all the way into the North and South poles. All moving charges feel a pull from a magnetic field if they are moving perpendicular to it. Because of this, when a moving charge out in space is moving perpendicular to the Earth's field lines, it gets sucked in, and because of the right hand rule, starts spinning around the field lines, right into the North and South poles. This is what causes the Northern Lights. We can only see them in the North and South poles because the charges are following the field lines into those poles, and that is where they are the most concentrated.  

How does a credit card machine read your card?

The credit card has a magnetic strip, which has a code. When swiped, the coils turn causing a current. The computer reads this current that is caused by the coils and counts the number of coils, letting the machine read your card. 

The right hand rule that I mentioned in the Norther Lights question, can be demonstrated in the picture:

The thumb represents the direction of the current of moving charges. The fingers curls around the thumb, representing the direction of the magnetic field. 

Electromagnetic Induction is the process of inducing voltage by changing the magnetic field of the loops of wire. The more loops in a wire, the greater the voltage is induced. Faraday's Law states that

the induced voltage in a coil is proportional to the product of its number of loops, the cross-sectional area of each loop, and the rate at which the magnetic field changes within these loops. There are three ways that voltage can be induced in a wire:

1. moving the loop of wire near a magnet

2. moving a magnet near the loop of wire

3. changing the current in a nearby loop

All of these methods involve changing the magnetic field in the loop of wire.

A transformer is a device used for increasing or decreasing voltage or transferring electric power from one coil of wire to another through electromagnetic induction. A transformer has 2 coils of wire. There is a primary, which is the input because it is directly connected to the power source. The other is the secondary. Electric current flowing through the primary coil causes a change in the coil's magnetic field. This spreads, inducing a voltage on the secondary coil. Voltage causes current, therefore, there is a electric current being transferred between the 2 coils. In order for the current to work, the transfer of electricity must be constant, and the only current that gives a constant surest is AC. AC current is constantly changing, while DC only goes one way, which wouldn't let the transformer work. 

Primary and secondary voltage relationship:

Primary Voltage    =   Secondary Voltage 

# of primary turns       # of secondary turns

energy is conserved, so power of primary = power of secondary. VI = VI. 

The last thing we learned about in this unit were motors and generators. Motors take electric energy (the input) and through electromagnetic induction produce mechanical energy (the output). Generators, on the other hand, take mechanical energy (the output) and with electromagnetic induction, make electrical energy (the input). Genorators produce a current as a result of motion. While the motor makes motion as a result of current.