Unit 7 Blog Post

Unit 7 Blog Post

            This was our LAST unit. This unit we learned all about magnetism; magnetic poles, electromagnetism, forces on charged particles in the electric field, motors, generators, energy production, transformers and energy transfer from a power company to a household.

            We began the unit by learning the basics of magnets. Moving charges are the source of all magnetism. All magnets have a north and south pole. The Earth has geographic poles (north and south) as well as a magnetic field with north and south poles. Domains are clusters of elections spinning in random directions. Domains that are aligned have a north and South Pole where as unaligned domains do not have north and south poles. If you cut a magnet in half it will have north and south poles on each half. The field lines inside of a magnet run north to south and the field lines outside of a magnet run south to north. Like poles of magnets repel and opposite poles attract. Like poles repel because the field lines are running in opposite directions where as opposites attracts because the field lines are running in the same direction.

            An example that explains many of these magnetism concepts, it explains why a paperclip sticks to a magnet. A paper clip is not always magnetized. Domains in a paper clip are random [domain is a cluster of electrons that are spinning in the same direction]. All magnets have 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 pole and a south pole and the north pole of the paperclip is attracted to the south pole of the magnet and thus the paper clip sticks to the magnet.

            When learning about magnetic poles we also learned about how a compass works and we learned about cosmic rays, which cause the northern lights. Northern lights are caused by cosmic rays. Cosmic rays that try to enter at the equator are deflected because they are perpendicular to the Earth’s magnetic field whereas at the poles, cosmic rays are parallel to the magnetic field, therefore they can enter the Earth. Cosmic rays are extremely dangerous to humans however because they shoot through human DNA causing serious health issues.

            Next we learned about electromagnetism. A current carrying coil of wire is an electromagnet. The number of turns in the coil increases the voltage of the wire which increases the current therefore strengthening the magnet.

            Following electromagnets, we learned about electromagnetic induction, which is the phenomenon of inducing voltage by changing the magnetic field in loops wire. The changing motion between a wire and a magnetic field induces voltage. The more loops moving in the magnetic field, the more voltage there will be making it more difficult to push the magnet into a coil (a greater resistance). It is a loop of wire in a complete circuit, a magnet is inserted through or around the loop of wire and that changes the magnetic field of the loops.  The induced voltage makes a current. This change in magnetic field induces a current. The amount of current produced by electromagnetic induction depends on induced voltage, the resistance of the coil and the circuit, and changing a current in a nearby loop. The current will be a signal. If we continuously change the magnetic field, that is how a generator works. Electromagnetic induction and generators turn mechanical energy into electrical energy and motors turn electrical energy into mechanical energy. [Mechanical energy is a magnet physically moving whereas electrical energy is current in the wire.] Electromagnetic induction is a part of our daily lives. It can be found in various devices such as metal detectors, traffic lights, credit cards, etc.

            In the pavement, 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. Metal detectors and credit card machines undergo a similar process.

Next, we also learned about how a motor works. This explanation can be found in my previous blog post.

We learned about both motors and generators. Motors and generators have almost identical construction but opposite roles. Motors turn electrical energy into mechanical energy, whereas generators turn mechanical energy into electrical energy. A key note to remember about motors is that 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. Motors can be used for cars, fans, blenders, etc. Generators use resources such as wind, water, steam, etc and 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.

We concluded our unit with transformers. Have you ever wondered about the little box in your computer charger? This little box is actually a transformer and is used to connect your computer to a wall socket allowing it to charge. We learned that transformer is a device used for increasing or decreasing voltage or transferring electric power from one coil of wire to another through electromagnetic induction. A transformer is simply two coils of wire. There is a primary coil and a secondary coil. The primary coil is connected to the power source so it is the input and the secondary coil is the output. Whenever the primary switch is opened or closed, voltage is induced in the secondary current. AC current is running through the primary, which causes change in the magnetic field. This changes the magnetic field of the secondary at the same rate. DC current cannot be used for a transformer because the current it produces only moves in one direction whereas the AC current continuously changes the direction of the current, which causes the change in the magnetic field. The number of turns in the wire is directly proportional to the voltage induced. The more turns in the wire, the more voltage there will be. The less turns the less voltage there will be. If the secondary has more turns the primary it will produce more voltage than the primary and the voltage will said to be stepped up. If the secondary has less turns than the primary it will produce less voltage than the primary and the voltage will said to be stepped down.

This formula shows the relationship between the primary and secondary:

[# of Primary Turns/Primary Voltage = /# of Secondary Turns/Secondary Voltage]

-The power in the primary is equal to the power in secondary.

[Power Primary=Power Secondary]

Note that [Power=CurrentXVoltage]

So [IV=IV] and the proportions change based on the levels of current and voltage

[Iv=IV]

*An Important Note: keep in mind is that the energy always remains constant due to the conservation of energy, it never changes.

This unit I particularly struggled with transformers. I was confused between the primary and the secondary and which one was the input and which one was the output. I overcame this by re reading my notes as well as further explanations in the book. Although we had to read those pages for homework, I was confused when I read them the first time. However, the second time I read about transformers, I was writing my podcast script so I was paying close attention to detail and was able to record all of it. I also realized it helped me to draw a picture of a transformer rather than to remember different variables in my head when solving a problem.

Although some of the quizzes I did not do as well on as I would have liked, I felt like this unit I clarified most concepts as I learned them. In other words, I understood concepts more easily in this unit than I have in previous units in part due to my persistence in fully learning each concept along the way. I think a part of this unit that really helped with my problem solving skills was the motor project. I had to understand how motors worked in detail, in order for my own motor to work. It was really cool to put my physics knowledge into action. Although I struggled with quizzes this unit, the quizzes helped me a lot. Most answers that I missed I got partial credit because I answered part of the question but not the other parts fully. I corrected these quizzes whenever I got them back and it helped me pay closer attention to the details that I was overlooking.

Podcast Video will be posted Wednesday, May 1.