Unit 7 Reflection!

This unit in physics we studied a lot of things relating to using motors, generators, and magnetism. We began with magnetism. We deducted that all magnetism is caused by current/moving charges. However, only charges moving in a given direction will cause something to be magnetic. This boils down to: Moving charges in a net direction will exhibit magnetic properties. This led us to once of the most important questions of Unit 7: Why does a paperclip stick to a magnet?

To start, we know that a magnet has domains spinning in a net direction simply because it is a magnet. We also know that the paper clips domains are spinning in random directions simply because it is not a magnet. The magnet has a magnetic field spinning around it, when the magnet comes close to the paperclip the domains of the paperclip start spinning in the same direction of the domains of the magnet. Now the paperclip is aligned with the magnetic field of the magnet. The paperclip now has a north pole and a south pole, the north pole of the paperclip is attracted to the south pole of the magnet, thus the paperclip sticks to the magnet!

From this question we can deduct a few things:

1)    The paperclip is now a magnet

2)    Opposite poles attract each other

3)    Like poles repel each other

Learning about magnets led us to talk about the Earth’s magnetic field. The Earth is actually a giant compass. The Earth, just like a magnet, has a north pole and a south pole, and all the charges move from south to north. The charges exit earth out the North Pole and circle back around earth into the South Pole. When the magnetic field surrounds earth, it actually protects it from harmful rays. We know this because all moving charges feel a force in a magnetic field when they are moving perpendicular to that field. For example, the northern lights, the northern lights only appear at the poles of the earth because that is the only place that cosmic rays are able to enter earth’s atmosphere. Thanks to earths magnetic field the cosmic rays can only enter the atmosphere at the poles because that is the only place that they are traveling parallel to the magnetic field. At the equator of the Earth cosmic rays are deflected because they meet the magnetic field at a perpendicular angle.

MOTORS:

One of the biggest activities of this unit was when we got to make our own motor! Making a motor was surprisingly a lot easier then I thought it would be. The materials we used were a battery, a magnet, a rubber band, two paperclips, and a coil of wire. The battery provided an electric potential difference so that there could be a current running through the coils. The coils, which were suspended above the magnet by the paperclips, would spin. The coils spun because current carrying wires are going to feel a force when in the presence of a magnetic field. The spinning coils were a motor. If we had attached wheels to either side of the wire then we would have a little car. Similarly, if we attached blades to the either end of the coils, we could have a blender or a fan. It is important to remember that with a motor we are putting electric energy in and getting mechanical energy out.

Right hand rules!

This unit we learned about two important right hand rules. The first tells us what way the magnetic field would wrap around a current carrying wire. The way your fingers wrap around your thumb represent the magnetic field while your thumb represents the direction of the current. The second right hand rule uses three fingers, your pointer, middle, and thumb. The middle finger represents the magnetic field; the pointer is the current, and the thumb the direction of the force!

A very similar concept to motors is generators, however they are the complete opposite. With generators we input mechanical energy and get electrical energy out of it. A generator works when a coil of wire is moved around a magnet or when a magnet is moved in and out of a coil of wires.

ELECTROMAGNETIC INDUCTION:

Electromagnetic induction is the reason that our credit cards work, metal detectors in airports work, and why stoplights change when cars drive up to them. When a car drives up to a stoplight there is a coil of wire in the ground. As the car drives over the coils of wire it induces a voltage. This voltage causes a current and this current acts as a signal telling the stoplight to change the light. The same thing goes for credit cards. A coil of wire is inside of the credit card machine. When the card is swiped the magnetic strip on the credit card changes the magnetic field and induces a voltage, which creates current, which acts as a signal and tells the computer the costumers credit card number.

TRANSFORMERS:

Transformers are those little boxes on appliances that either step up voltage, or step it down. In a transformer there is a primary coil and a secondary coil. The loops of the primary coil divided by the voltage going into the primary coils is equal to the secondary number of loops divided by the voltage going into the secondary coils. We know the power of the primary is going to equal the power of the secondary. However, depending on the type of transformer, the primary number of loops is going to be greater or lesser then the secondary number of loops and the opposite for the voltage. A mathematical equation could be written as 1 # of loops/1 volts = 2 # of loops/2 volts.

Some important formulas to remember for this unit would be:

P=IV (Power = (Current)(Voltage)

I=V/R (Current = Voltage / Resistance

*An important thing to remember for this unit was that when talking about generators, only Alternating Current works in order for electrical energy to be the resulting output. This is because with Alternating current, the alternating movement of electrons causes a change in the magnetic field, which is the catalyst for the flow of current. With Direct current, the electrons only flow in one direction, the lack of change would cause no change in magnetic field and a current would not be created.

PODCAST: