Unit 7

We learned four main concepts during unit 7, they are, how charges and poles work and are seen in our world, motors, electromagnetic induction, and transformers.


Poles!

There is a North Pole and a South Pole, and in almost every object there are domains. A domain is a cluster of electrons in an object. When something is un magnetized the domains in that object are completely random. However, in order for something to be magnetic, the domains must all line up and point in the same direction. This can be seen in the diagram below.

Magnetism are all moving charges!

Once something becomes a magnet, it will have a magnetic field like so.

When two poles are next to each other they will repel because the domains would be pointing at each other --> <-- therefore colliding and pushing away. When two opposite poles come close to one another the domains line up and are able to run throughout the whole magnet.




How does one make a paper clip into a magnet?
The domains of a paperclip are random making it unmagnetized. However, when the magnet comes in close contact with the paperclip the domains begin to shift and point towards the N pole of the Magnet, once they all are pointing in the same direction the paperclip becomes a magnet! Therefore the paperclip has its own magnetic field and opposite poles attract so the magnet and paperclip connect to one another!

Motors

A motor is made up of two things, a current carrying wire and a magnet. The current carrying wire feels a force and the magnetic field will cause torque. Moving charges must be perpendicular to the magnetic field of the magnet to be repelled, thus the wire must be perpendicular. We also see this with cosmic waves, or Northern lights!

As you can see in this diagram to the left Earth's magnetic field creates a "shield" against moving charges that are perpendicular. However, when a charge comes parallel to Earth's magnetic field it will enter the atmosphere, theses are called Northern lights! and they only occur at the poles for that reason!

The right hand rule is a rule anyone can use that has their pointer and middle finger plus a thumb on their right hand, that's it! The pointer finger represents current, middle finger represents the magnetic fields, and the thumb represents the the direction of the force.


A motor transfers electrical energy to mechanical energy and relies on the fact that a current carrying wire will feel a force in a magnetic field. The current carrying wire must be perpendicular to the magnet's magnetic field or the wire will not spin. However, a generator transfers mechanical energy to electrical energy with electromagnetic induction that then induces voltage in coil to cause causes current, but still uses coils of wire and magnets.


Electromagnetic Induction

Electromagnetic Induction is the process of inducing voltage that then causes current. It occurs when a magnet/s is pushed through a coil of wire, that changes the magnetic field in the loops of wire. (So no battery needed) The greater the number of loops of wire the greater the voltage. We know this because of Faraday's law, induced voltage in a coil is proportional to the product of the number of loops. 

How does a credit card machine work?
In a credit card machine there are a series of coils of wires that when the credit card is swiped through is induced by the magnets inside the magnetic strip on the card that then causes a current. This specific current signals to the credit card company and gives the credit card number for that card. Boom.

How does a metal detector work? 
In the metal detector there are coils of wire. When a metal object passes through the metal detector it interferes with the coils of wire's magnetic field that induces a voltage that then causes a current which causes an alarm to go off.



Transformers

Transformers are used in everyday life, they can either increase the voltage needed for an appliance like a washer or dryer, these are known as step up transformers. There are also appliances that need a lower voltage than the normal wall outlet lets out, like a computer, these are know as step down transformers.

In these two transformers, there are a two coils of wire. For a step up transformer the number of loops in the wire in the secondary coil will be larger than the primary coil and vise versa for a step down transformer. We know this because of Faraday's law, induced voltage in a coil is proportional to the product of the number of loops. 

All transformers rely on AC so the magnetic field of the primary coil is constantly changing. Without it the magnetic field of the primary coil of wire would not change, therefore the village will not be induced and there will be no current, so nothing gets to the appliance.

The equations that help us figuring out information with transformers are:
 # if Turns in 1/voltage in 1=  # if Turns in 2/voltage in 2. This equation helps us determine if the transformer is a step up or a step down.

I(V) of primary= I(V) of secondary

Power companies often use step step up transformers in order to save energy that would normally be lost by heat.

With that let's do some problems!                                                                                                

1a)A transformer is used to connect my computer to the wall socket. The computer requires 20V and the wall socket provides 120V.

b) If the primary coil of the transformer has 70 turns, how many will the secondary coil have?

70/120=x/20 x=11.66 loops!

c) If the computer runs on a 2 A current, what will the current drawn from the wall be?

(120)(x)=(20)(2)
120x=40
x=40/120