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. 

Motor Blog

Motor Blog:

There are a few key parts to the creation of the motor made in class; a battery, a coil of wire, a paperclip, and a magnet. The battery provides the current allowing the motor to function. It uses electrical energy to become mechanical energy. The coil of the wire or the motor loop carries the current. The coil of the wire feels the force causing torque. [A current carrying wire feels a force in a magnetic field and force can cause torque]. The paperclip completes the circuit; it carries the current to the wire (which is a part of the motor loop).  The magnet provides the magnetic field.

A motor is a current carrying wire that feels a force in a magnetic field. The more wire and the stronger the magnet, the stronger the force. This force comes from the motor loop deflecting the magnetic field. The coil of the wire has been shaved on one side on both ends so that the current in the coil of the wire flips the direction with each half turn in a continuous direction creating a motor.

You could potentially put small wheels on either side of the motor loop and the simple motor I made could be used as a miniature car. It could be a new type of mouse car project, where you create a miniature car to show your understanding of multiple physics concepts such as torque and magnetism. The motor would function identically to the paragraph described above. I would use more wire and a stronger magnet however, so that the car could experience a greater force therefore move at a faster speed.

To the right is a picture of a simple electric motor similar to the one I made in class. It has the labeled parts as well as the direction of the current.

Magnetism Source

http://www.youtube.com/watch?v=ak8Bh9Zka50

            This source was particularly useful in explaining the basics of magnets. I liked how it explained that the Earth has a magnetic field and that all magnets have a north and south pole no matter what. One interesting part of the video was when the boy was pretending to take away the paper clips with magic when really he was using a magnet to pull the paper clips away. 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.

Unit 6 Blog Reflection

Physics Unit 6 Blog Reflection

            This unit we learned about major physics concepts involving electricity and more specifically; charges, charge transfer, polarization, electric fields, Coulomb’s Law, electric potential difference (voltage), current, types of current, source of electrons, Ohm’s Law, power, parallel circuits, and series circuits.

             Electricity a term used to represent a wide range of electrical phenomena that underlies everything around us. In order to understand a small portion of this huge part of life, we dissected it into different concepts. We began with electric charges. A charge can either be positive or negative. Protons have a positive charge and electrons have a negative charge, neutrons do not have a charge. Like charges repel; opposite charges attract. The transfer of electrons from one place to another causes charge. There are three ways for this transfer to happen; direct contact, friction or induction.  Direct contact and friction are self-explanatory for the most part. However, induction is a little bit more complex.  Induction happens when you bring a charged object near a conducting surface.

            Lightning is a good example of induction. Charging by induction takes place during thunderstorms. The clouds are negatively charged by friction and the clouds positively induce the ground.  The attractive forces eventually become strong enough to produce lightning. Therefore lightning starts from the ground, travels upward and then recedes toward the ground. This example also includes the idea of conductors versus insulators. Lightning rods are conductors. The main purpose of a lightning rod is to prevent a fire caused by lightning. Lightning rods are sharp, tall, and filled with positive charges. It will direct the lightning to the rod and to the ground rather than to the structure. The lightning is conducted into the ground rather than the house. Conductors allow the flow of electrical charge and insulators prevent the electrical charge. 

            Then, we learned about polarization. Induction can be found with conductors as well as insulators. Polarization is the separation of charges. A polarized object is still neutral because the charges are only separating; the electrons are not increasing or decreasing. An example we learned about that explains this as well as Coulomb’s Law is the reasoning behind why plastic wrap sticks to a ceramic bowl. The plastic wrap is charged by friction and when brought near the bowl, the bowl polarizes. The positive charges in the bowl move close to the negative plastic wrap and the negative charges in the bowl move away from the plastic wrap. The distance between the opposite attractive chargers is smaller than the distance between the like repelling charges. Coulomb’s law states that the force between any two charges are inversely proportional to the distance. F=kq1q2/d^2 Because there is a greater distance between the repulsive forces, the forces between them will be less than closer attractive forces. Therefore, the plastic sticks to the ceramic bowl. 

            Electric field is the area around the charge that can influence another charge. We draw electric fields in which direction a positive charge would pull. The closer the lines are together the stronger the electric field. The farther away you are from an electric field, the weaker it is. It is important to remember the difference between electric fields and gravitational fields is that various materials can shield electric fields, whereas gravitational fields cannot be shielded. Metal can completely shield an electric field. The electric field inside the metal encasing will feel no force by any charges outside of the shield. The filed inside will field no force no matter what. This is often why electronics are encased in a metal shield, so that the device inside of the metal case will feel no force outside of it, therefore it can function. 

            Next, we learned about the importance to know the difference between electric potential and electric potential energy. A charged object has potential energy through its location in an electric field. Electric potential energy is the energy a charge has due to its location in an electric field whereas electric potential, otherwise known as voltage and measured in volts, is equal to electric potential energy (in joules) over the charge (in coulombs). V=PE/Q.

            Following this we learned about electric energy storage. A capacitor is a common device where electric energy can be stored.

            The difference in potential energy is when the ends of an electrical conductor are at different electric potentials, charge flows(charge flowsàwhich is current) from one end to the other. The flow of the charge continues, as along as there is potential difference. When there is no potential difference, no charge flows. Charge flows when there is a high voltage and a low voltage and will stop when they are both an equal voltage. The rate of electrical flow, current, is measured in amps. Current will only work if there is a difference in electric potential. A key note to remember is that voltage causes current. Current does not cause voltage.

Take batteries for example. Batteries are able to have current because they have a difference in electric potential or a difference in voltage. Overtime, the difference decreases and eventually there is no longer an electric potential difference. When there is not an electric potential difference, there is no current, which is why batteries stop working.

Another example explains why flashlights get dimmer as the battery becomes weaker. A flashlight gets dimmer as the battery becomes weaker because the difference in voltage decreases, voltage causes current and the less current there is to light the bulb, the dimmer it will be.

Also, the idea that to complete a circuit, there must be current. This current comes from the potential difference from the high voltage to the low voltage. This is why birds aren’t harmed when sitting on a power line wire. If birds are standing on only one wire, they are not completing the circuit because they aren’t touching the ground (which would conduct electricity through their bodies and into the ground) and they aren’t touching the two wires at the same time. This means there’s no current meaning that there is no electric potential difference.

The amount of current that exists depends on the voltage as well as the electrical resistance, the conductor, which offers the flow of charge. The resistance of a wire depends on the thickness, length, and material. The thicker, the shorter, and the better conductor material, and the colder the wire is, the wire is the less resistance there will be meaning there will be more current. Electrical resistance is measured in ohms. 

Ohm’s law states that current in a circuit is directly proportional to the voltage and is inversely proportional to the resistance of the circuit. Current(amps)=voltage(Volts)/resistance(ohms)

Electric shock can be damaging from the current passing through the body. This current that runs through your body depends on both the voltage used and the electrical resistance of the body. To receive a shock, requires a difference in electric potential from one part of your body to another part. As long as you are wearing some sort of insulator or you are standing on an insulator, or you are not completing the circuit, you will not feel any shock not allowing the current to run through your body.

Another key factor to keep in mind is that “high voltage” does not necessarily mean high danger; the danger factor rests upon the amount of stored energy there is.

Look at this plug, the round prong connects the rest of the appliance directly to the ground. Any charge built up on the appliance is then conducted to the ground, which prevents accidental shock. We briefly discussed direct current and alternating current. Electric current can come in two forms; dc or ac. DC is direct current, which refers to the flowing of charges in ONE direction. A battery uses direct current. AC is alternating current, which moves in one direction and then the opposite direction and moves in this path continuously. Households use AC current.

            Think about flipping on a switch to a light in a room. The lights work immediately when the circuit is completed. Current is established through the wires at nearly the speed of light. It is not the electrons that are moving quickly, in fact the electrons are moving very slowly but the electric signal moves nearly at the speed of light. Another misconception about electrons is the idea that electrons flow from the outlet into a lamp but it is actually, when you plug a lamp into an outlet, energy flows from the outlet into the lamp.

            Moving onto electric power, electric power is equal to current times voltage. P=IV and the relationship between energy and power is simply. Power=Energy/Time

            The last concept we covered was electric circuits. A circuit is any path along which electrons can flow. There are two types of circuits; series and parallel. A series circuit has all devices connected end-to-end, which forms one path for electrons to flow. The more appliances added the more resistance increases, current decreases, brightness (power output) decreases, and when one light bulb stops working or is removed, they all stop working. A parallel circuit has electrical devices connected to the same two points. The pathway for current from one end of the battery to other is completed if only one light bulb is lit rather than all light bulbs in the circuit.  The more appliances or light bulbs added to the circuit the resistance decreases, the current increases, the brightness remains constant and when one light bulb stops working, the rest are not affected. Households use parallel circuits because it is more efficient. Parallel circuits allow households to run multiple devices without running other devices unlike series where it is all or nothing. The only major disadvantage to parallel circuits is the heat factor. The more current and less resistance there is (which happens the more devices are on), there is high heat, which could potentially turn into a fire. A fuse/circuit breaker prevents this from happening. A fuse is used to prevent the current from getting to this dangerous level. The fuse melts and snaps turning the circuit off. A fuse is used in parallel circuits but it is set up in series. 

            This unit has been particularly challenging for me. I struggled with understanding each and every concept we learned to its fullest because there were so many concepts to go over. I became frustrated with learning the process of lightning, capacitors, and the difference between electric potential and electric potential energy. The confusion with these concepts lead me to not do as well on quizzes that I would have liked. 

             However, I overcame these struggles by taking each concept step by step. I went through the book and looked the examples used and compared them to my notes. I was able to use more detail with the examples and have a better understanding of each one. Also, I went through each quiz and corrected what I got wrong so that I could understand it more clearly and not mess up on the test. 

             My problem solving skills this unit were slow but comprehensive. I tried my best to understand the material I was unclear about. I went in for help various mornings, usually before quizzes. I always completed my homework in detail and corrected my answers in class if I got questions wrong. I think labs were particularly useful for me as well as group work because our groups could bounce information and answers off one another without a group shutting down the other group. 

            

Unit 6 Photo

            Have you ever taken a balloon, rubbed it on your head and put it on the wall and it stuck to the wall? Well, this unit, I learned the physics behind this. Notice in the picture the balloons are sticking to the wall. The balloons were charged with friction when they were rubbed on people’s hair and were given a negative charge. When one of these balloons is brought near the wall, the wall polarizes, meaning the positive charges in the wall move close to the negatively charged balloon and the negative charges in the wall move away from the balloon. The attractive charges will be closer together and the repulsive charges will be farther apart. Coulomb’s Law, F=kq1q2/d^2, states that force is inversely proportional to the distance and directly proportional to charges. Therefore, the attractive charges have a greater  force because their distance is smaller which is why the balloon sticks to the wall.

Although the picture above demonstrates a real life situation when the balloon sticks to the wall, here is an animated version that can show the explanation of polarization and the difference forces.