Magnetism Unit Blog Post

In this unit I learned about:

1. Magnetism; magnetic poles; electromagnetism
2. Forces on charged particles in an electric field; Motors
3. Electromagnetic induction and common applications
4. Generators and energy production
5. Transformers and energy transfer from power company to home

Magnetism; Magnetic poles; electromagnetism;
Magnetism refers to the force between magnets. Objects that produce magnetic fields will have poles that will attract or repel other magnets (like poles repel and opposites attract). The source of all magnetism is moving charges.

Like poles repel because the magnetic field lines are in opposite directions which causes them to repel. The magnetic field lines show the direction of the field at different points.

The field lines between the two like poles diverge.

Opposite poles attract because their field lines line up in the same direction. Note how the field lines enter in from the south pole and out through the north pole

One of the major questions we were asked about magnetism was; Explain and who how you turn a paper clip into a magnet?

The Answer is because the cluster of atoms in a paper clip have electrons that are spinning in the same directions, this is referred to as the magnetic domain. But the domains are pointing in deferent directions at different times. Below is an image showing what the domains look like between a unmagnetized object and a strong magnet.

When the paper clip is placed in proximity to the magnet, the domains within the paper clip align with the magnet thus making it a magnet with a north and a south pole. The paper clip is now attracted to the magnet because they are in the same magnetic field, due to the fact that opposite poles attract.

Forces on charged particles in an electric field:

The rule that we learned with this topic is called the right hand rule. When a charges is placed in a magnetic field that charge feels a magnetic force. The charge moves relative to the magnetic field, and the charges velocity is perpendicular to the direction of the magnetic field. This causes the particle to spiral around the magnetic field. Here is an image showing you how it works.

The thumb represents the force and your other fingers represent the magnetic field which is drawn withe the vectors.
Another main question regarding the force on charged particles in an electric field is what causes the northern lights?
Like magnets the earth also has a north and south pole, but what we know geographically to be the north pole is actually the magnetic south pole and the geographical south pole is actually the magnetic north pole. Here is an image of the geographical poles and the magnetic poles of earth.

Therefore since the magnetic field deflects cosmic rays from traveling through to earth they instead spiral around the magnetic field and enter in the south magnetic pole. This is why there is more cosmic radiation in the north than in the equator. The spiral motion can be seen in this image.

Electromagnetic induction: is the phenomenon of inducing voltage by changing the magnetic field in loops of wire. Voltage is induced in a wire when either the magnetic field moves past the wire or the wire moves through the magnetic field. This concept can by understood through Faraday's Law which states: The induced voltage in a coil is proportional to the product of the its number of loops (more loops means more voltage), the cross-sectional area of each loop, and the rate at which the magnetic field changes within those loops. Because more loops mean more voltage it takes more work to induce it. For example pushing a magnet into a coil with many loops is difficult because the magnetic field of each loop resists the motion of the magnet.

Generators and energy production:

A generator is when voltage is induced by moving a coil than by moving a magnet. The arrangement of rotating coil in a stationary magnetic field is called a generator. A motor and a generator are basically the same thing, for the only thing they differ in is the roles of their input and output are reversed. In a motor electric energy is the input and mechanical energy is the output. While in a generator mechanical energy is the input and electric energy is the output. But both of the devices transform energy from one form to another. Because the voltage induced by the generator alternates, the current produced is ac.

Transformers and energy transfer from power company to your home:
A transformer is a device used to reduce (step down) or increase (step up) voltage of an alternating current. In a transformer there is a primary and secondary source. The primary source is connected to the power source and only induces voltage in the secondary source when the magnetic field is changing through the coil. If the secondary coil has more turns than the primary source, the alternating voltage produced in the secondary coil will be greater than the voltage in the primary (step up).

Transformers are used by power companies to slow down the current. Companies want the current in the power line to be low because then energy doesn't go to waste in the form of heat. When current is high the wire heats up, but by increasing the voltage the current decreases. This is possible because power in the primary is equal to the power in the secondary.

Power (primary) = Power (Secondary)

VI = VI

As voltage increases current decreases and vis-versa.

One of the main questions asked was how do credit cards work?

The answer is that a credit card has a magnetic strip that has sectors that are magnetized in different ways following a code. The reader has a lot of different coils that are induced with voltage when put through the swiper. The computer interprets the electric signals back to codes.

What I have found difficult about what I have studied in this unit was the equations problems.

If a machine requires 10A current, what will the current drawn from the wall socket be? (Wall socket provides 120V)

Power (primary) = Power (secondary)

(120v)(I) = (

What made the lightbulb click was getting the problem wrong on the quiz, because being able to compare my mistake to the correct answers made me understand the problem more clearly. My persistence in class is pretty consistent. I work to turn in every homework assignment on time and when I don't understand a certain topic I make a conscious effort to come in during conference period to ask question. I have no goals for the next unit because this is our last physics unit of the year. A connection that I made between what we studied and everyday life was how a credit card reader is able to receive money from my credit card.