Unit 7 Blog Reflection: Magnetism

Magnetism: 

Finally we have reached the end of the line. The last unit of our regular physics course was on magnetism. The first thing we learned was that the source of all magnetism comes from moving charges.

All magnets have a north and south pole, and their field lines run from north to south inside, and south to north outside. If the magnet is cut in half, it too will form a north and south pole. The Earth is similar in that it has a geographical north and south pole as well as a magnetic field which works the same as a magnet. There is physics behind a compass, because it is a little magnet that can spin freely. The north end of the magnet attracts to the south end of the earth, whiles the south end of the magnet, attracts to the north end of the earth. This attraction causes the needle to align with the earth's magnetic fields. The north pole of the compass points to the correct geographic north because the earth's geographical poles differ from the earth’s magnetic poles.

If something is magnetic or has become magnetized it means that their domains have aligned. Just like vectors add, so do domains. A magnetic field is an area that has become magnetized, and is created when a particle is moving perpendicular to the direction of the fields magnetic force.

The big question for this section was; how does a magnet pick up a paper clip? Domain in the paperclip is random. A domain is a cluster of electrons that are spinning in the same direction. The magnet has a magnetic field. When the Magnet is close to the paperclip thee domains of the paperclip align to match the magnetic field of the magnet. The paperclip now has a north and south pole and the north pole of the paperclip is attracted to the south pole of the magnet and thus the paperclip sticks to the magnet.

The next thing we learned was about motors. We learned about motors by making mini-models which couldn't actually be used a source of power. The motors we made consisted of a battery, paperclips a coil of wire, and a magnet. (the motors we made were similar to the model shown below)

 

When the battery runs a current through the system, the magnetic field creates a torque on the coil which causes it to rotate. You need an AC current for this motor to work, or for most any motor. Motors transform electrical energy into mechanical energy. Moving charged particles feel a force when moving perpendicular to a magnetic field. The force felt by the wire causes a torque. Motors work from the force of the magnetic field.

Magnetic induction is when a magnetic field is created by running a current through coils.

 Electro-magnetism is using magnetism to create electricity. This is found in transformers. A transformer is a device used for increasing or decreasing voltage and transferring electric power from one coil of wire to another through electromagnetic induction. A transformer is made up of two coils of wire; primary and secondary. The primary is the wire directly connected to the power source. The secondary wire is the wire closer to the device being charged. Therefore, the primary is the input, the secondary is the output. Whenever the primary switch is open or closed, voltage is induced into the secondary current. Alternating current (AC) runs through the primary, which causes a change in magnetic field. Direct current (DC) cannot be used, because the current it produces only goes in one direction.

There are two types of transformers; a step up and a step down transformer. They are based on how many turns of a coil each transformer has. If the secondary has more turn than the primary this is considered a step-up transformer, but if the secondary has less turns than the primary it is considered a step-down transformer. The equations for transformers are:

v  Primary Voltage/primary Number of turns = Secondary voltage/ secondary number of turns

v  power is always conserved, power in = power out

v  Voltage x Current= Voltage x Current

v  VI in = VI out

These equations are used in power companies to minimize loses. This is because they can increase the voltage to decrease the current which decreases the loss of electricity to heat.

Electro-magnetism is the physics behind how a credit card machine works; hence the next big question was how does a credit card machine work? A credit card has a magnetic strip. There is a code on the magnetic strip. When the card goes into the reader voltage/current is induced due to the coils of wire which when reacting to the credit card change the magnetic field. The computer interprets electric signals back and forth which ultimately read the card.

Generators have similar design to motors, only its role is reversed. A generator will store mechanical energy as electrical energy. Through electromagnetic induction, generators turn mechanical energy into electrical energy. Generators use resources such as wind or water to turn loops of wire inside of a magnet. 

It relies on the change in the magnetic field rather than the force of the magnetic field. This change in the magnetic field induces voltage which causes current, which is the current we tend to use in our households.

Electromagnetic induction is a way to increase voltage by changing the magnetic field in loops of wire. The change between a magnetic field and loops of wire is what induces voltage. The more loops in a magnetic field, the more voltage, subsequently, the more resistance. When the magnet is inserted through or around the loops, there is a change in the magnetic field of the loops. The induced voltage also means an induced current. The amount of current produced in electromagnetic induction depends on induced voltage, the resistance of the coil and the circuit, and the change in current in a nearby loop. 

Real life applications:

v  In the pavement, at a stoplight there is a loop of wire. When the car, which is magnetic, moves over the wire, it changes the magnetic field of the loop. This change in the magnetic field induces voltage, which causes a current. This current is a signal to the stoplight to change.

v  Metal detectors

v  credit card machines

Conclusion:

The hardest part of this unit for me was to understanding so much material in so little time; especially with creating the motor and understanding the function of all its parts. 

My strongest part of this unit was when we got to transformers and electromagnetic induction, because although I didn’t know the terminology this was information that I kind of already knew. For the test, I will review my notes and the review sheet which we went over as a class.