Magnetism

In this unit we learned about (the order is weird but just go along with it)

• Magnetism; magnetic poles; Electromagnetism
• Forces on charged particles in an electric field; Motors
• Electromagnetic induction and common applications
• Generators and Energy Production
• Transformers and Energy transfer from Power company to Home

Electromagnetic Induction
-Changes the magnetic field of a loop of wire
-Induces voltage
-Causes current

For example, electromagnetic induction is happening when a traffic light at an intersection is changed when a car approaches. In the concrete there is a coil of wire. When the car rolls over this, the coil's magnetic field is changed. This induces a voltage which causes current. This current signals the light to change.

In a credit card there is a series of magnets. There are coils of wire in the machine. The pattern of magnets change the magnetic field of the wire. This induces a voltage which causes a current. This signals the credit card number thus charging your card.

Transformers
-A transformer is used to increase or decrease the voltage from the wall in order to apply the right amount of voltage needed for an appliance or device.
The primary must have an alternating current (AC) which means the magnetic field of the primary is always changing. Because of this, the magnetic field of the secondary will change as well. It induces a voltage. This causes a current. You find the transformer in an appliance that needs either more or less voltage then the wall supplies. There are two kinds- a step up and a step down. Step ups are used when the voltage given from the wall needs to increase and step downs are used when it needs to decrease to fit the appliance.
Faraday's law states that "the voltage induced is directly proportional to the number of loops".
-It consists of two coils of wire, a primary and a secondary. In a step up the secondary more coils and less in the primary. In step down there are more in coils in the primary than the secondary.
1. A washing machine requires 1600V to work and the wall socket provides 160V. What type of transformer is required?
-Step up
If the primary coil of the transformer has 10 turns, how many will the secondary coil have?

loops primary = Loops secondary

V primary V secondary

10 = x

160 1600

160x = 16000

x=100 coils

If the washing machine requires 100A current, what will the current drawn from the wall socket be?

Power of Primary= Power of Secondary

IV=IV

(160)(I) = (1600) (100)

(160)(I)=160000

I=160000/160

I= 1000 Amps

Right Hand Rule

The right hand rule allows you to know the direction of the force. For example, if a wire in a current is running towards the right of the screen and the magnetic field ran up to the top then the wire will be forced into the screen.




Generators
-Made of coils of wire and magnets
-Goes from mechanical energy to electrical energy
-Electromagnetic Induction
-Spinning magnets
-Induces V in coil
-Causes current (I)

Motors
-Made of coils of wire and magnets
-Goes from electrical energy to mechanical energy
-Rely on the fact that a current carrying wire feels a force in a magnetic field.
-Torque

Magnetic Fields
-The source of all magnetism is moving charges.
-Not all charges have magnetic fields, they have to be moving in order to have one.

• Current Carrying Wires move like this- if the current is moving to the right, the force goes in this direction (black arrows)
  

• Permanent Magnets

The picture on the left shows unmagnetized domains and the right shows one that is magnetized.  A domain is a cluster of electrons that are spinning in the same direction. The one to the right shows that it has north and south poles (moving from south to north). This is magnetized and therefor has a magnetic field.
-Like poles repel and opposite poles attract. Like poles repel because their field lines are moving in different directions and force each other away. Opposites have field lines moving in the same direction. Thus, they attract.
-A compass is a magnet that is free to move

Why do paperclips stick to magnets and each other?
Domains in a paper clip are random. The magnet has a magnetic field. When the magnet is close to the paper clip, the domains of the paper clip align to match the magnetic field of the magnet. The paper clip now has a north and south pole. The magnetic field lines move from south to north on the inside and then move north to south on the outside. And the south pole is attracted to the north. Thus, the paperclip sticks to the magnet.

Why do cosmic rays only enter the Earth's atmosphere in the North and South poles?
Cosmic rays enter there because it will only feel a force and be repelled if they are in a perpendicular position to the magnetic field. So, when the rays are parallel and can enter the atmosphere at the poles, they will enter the Earth's atmosphere. (northern lights)