Top Ten Physics Concepts When Traveling Home

Before I took physics, a trip to the airport was boring. I'd walk in, go through security, and head to my gate. I'd sit there and simply play on my phone, bored out of my mind with nothing to do. Now when I walk into an airport, the building becomes a fun academic game. I try to see how many physics concepts I can identify and fully understand. Here are my top ten places/times I find physics concepts when I travel home...

1.) Chugga Chugga Toot Toot

2.) Checking Baggage 

3.) Going Through Security 

4.) Towing my Carry-on to the Gate  

5.) Going Up the Broken Escalator

6. ) Turning Without A Warning= Awkward New Friend 

7.) Trying to Stand Up with my Backpack  (It weighs more than I do, I'm convinced.)
NEED TO FINISH!!!!!!  

8.)  Up the Ramps They Go.  

9.)  Driving Past A Wreck On The Highway.

10.) Mom said, " Let there be light!" 

Part One: Chugga Chugga Toot Toot ! 

     There are a lot of trains here in Asheville, North Carolina. Usually, when I'm heading to the airport, we pass by some train tracks with trains chugging along. The part I now notice the most about the train are the wheels. It reminds me of when we learned about tangential and rotational velocity. Tangential velocity is the direction of motion tangent to the circumference, the linear speed of something moving along a circular path. It is dependent on the radial distance from the axis of rotation and is measured in m/s or km/s. It is also directly related to rotational velocity. Rotational velocity involves the number of rotations or the number of revolutions per unit of time. It is measured in RPM's (Revolutions Per Minute) and all parts of the wheel share the same number of rotations.

   Once I had learned that, I thought I knew how a train's wheels work and how they stay on the track. Sadly, I did not. It is actually the design of  the trains wheels that makes them stay on the track. The train's wheels are tapered so that the fat/wider part is on the inside with the more narrow part on the outside. All parts of the wheel have the same rotational speed, but the wider part has a greater tangential speed. It is this difference that causes the wheels to curve when the wider part is on the outside of the track. The wheel curves inward, setting the train back on the middle of the track.  It's already a great day for travel when I get to begin with this!

Part Two: Checking Baggage

     My next exhilarating moment comes when I check my luggage. When checking one's luggage, you have to set your bag on a scale at the check-in desk. Once you set the bag down, the bag is at rest on the scale. According to Newton's First Law (Law of Inertia) which states that, " an object at rest or in motion will remain at rest or in motion, until acted upon by an outside force." In this case the object is my overpacked bag that is at rest. The bag will remain at rest until acted upon by an outside force such as the check-in airport employee. Once they act on the bag (i.e they pick it up move it off of the scale), the bag will remain in motion until acted upon an outside force. In this case, that outside force would be the ground. 

Part Three: Going Through Security 

    When going through security, you are required to walk through a metal detector. If you hear the metal detector "beep," that "beep" is because of electromagnetic induction. Electromagnetic induction is that act of inducing a voltage by causing a change in the magnetic field of the loops of current carrying wire. Electromagnetic induction occurs when loops of current carrying wire experience a change its magnetic field when a magnet goes through, near, or around the loops of current carrying wire.
   
     The change in the current carrying wire's magnetic field induces a voltage, which causes a current that sends a signal that can be used for a variety of things. In the case of a metal detector,  the loops of current carrying wire are inside the plastic walls. If you have magnetized metal on you when walking through, there is a change in the magnetic field of the current carrying wires. The change in its magnetic field induces a voltage, which causes a current. This current sends a signal that sets off an alarm to let the TSA know that you may have a dangerous item on your person. 

Part Four: Towing my Carryon to the Gate 

   When I tow my carry-on to my gate, I can see an example of Newton's Third Law which states that, " For every action there is an equal and opposite reaction." In this situation, all of the action-reaction pairs are equal and opposite. An action- reaction pair is two objects with the same action such as "pull" or "push." However, they have different reactions. For example, one might have "forwards" while the other has "backwards." Action-reaction pairs are also only equal and opposite within themselves and not in comparison to another action-reaction pair. (see picture below)

Now you might think that it is how hard my pull is, is what causes my bag to move forward. In reality, it is how hard I push on the ground that will accelerate my bag towards me.

Part Five : Going up the Stairs to my Gate  

  I will admit, I'm not always the most patient traveler. I like to get where i'm going quickly, in hopes of getting some work done to one day have power. Therefore, if the escalators are clogged,  I will take the stairs. Now that i've taken physics, it turns out that I am already doing work and have power. In physics, the formula for work (measured in joules)(responsible for power)  is

Work= Force x Distance

The relationship between force and distance has to be parallel in order for work to be done. In addition to that, distance has to be covered when force is applied or else no work is done.

Now let's look at power.  The formal for power is Power= Work/Time. It is measured in watts. Here is an example...

Part Six: Turning Without a Warning = Awkward New Friend 

  Sometimes flights are peaceful and relaxing, while at other times they are bumpy and like a roller coaster. When walking down the aisle toward the cockpit, sometimes the pilots have made unexpected turns and I end up in a strangers lap.  I never considered why I went the direction or the force that caused it, my first thought was how to apologize to the persons lap i was now in. Now all I think about it centripetal and centrifugal force. Before I get into centripetal, I must explain that centrifugal force isn't real, it is a fictitious force. However, centripetal force is real. It is a center seeking force, therefore it acts in the inward direction. On the other hand, the plane's velocity is tangent to the circle. It is the combination of these two that makes for a very awkward way to meet new, but at least I get a good story out of it.

Part Seven: Trying to Stand Up with my Backpack

  Living far away from home and going to an elite boarding school adds up to a heavy backpack. when traveling home.  Before I learned about torque and center of mass, I'd stand straight up and lean back when getting out of my seat with my heavy backpack. This usually resulted in me falling straight back into my seat, almost taking my fellow passenger out with my bag. Now those embarrassing days are behind me thanks to this physic concept. 

Here is what I learned.... 

  I learned that the center of mass is the average point of an object's mass. The center of gravity is the specific point gravity act upon. If something is balanced the clockwise and counter clockwise torques are equal. See the diagram below... 

  Torque causes rotation. The formula to find an object's torque use the formula Torque= Force x Lever arm. A lever arm is the distance from the axis of rotation to where the force is applied. The only way to have a lever arm is if the center of gravity is not above the base of support.  In order to be balanced/stable I'd need low center of gravity, a wide base of support, and equal weight. On humans, our center of gravity is around where our belly button is. To lower my base of support, I then have to bend my knees. Then I must lean forward to make sure I keep my center of mass above my base of support. In doing so, I will not have a torque therefore there will be no rotation and I will not rotate outside my base of support. In turn, I will remain standing and walk out with grace and a slight turtle look. 

  In the picture the red x is where my base of support is. As you can see, my legs are bent and my base of support is low. My center of gravity is above my center of mass, therefore I have a force (marked by the blue arrow pointing down), but not a lever arm. In turn, I do not have a torque and will not fall over. 


Part Eight: Up the Ramps They Wheeled.

  As you may know, Florida is known for is being a great place to retire. So often when exciting the airport there are elderly people either arriving or departing. They are often in wheelchairs and have to use the ramps. Before physics, I just stared at the ramp and saw a block wood or metal. I didn't think much past that. Now I understand that it is actually a machine. It is a machine because a machine decreases the amount of force by increasing the distance. To find the amount of work a machine, like a ramp,  does you use the formula...

 Workin= Workout

  Fin x din = Fout x dout 

Ramp 

Labeled Ramp 

The F= force and d= distance.  Here is an example of something I might see... 

Now to find out how efficient a machine is, you use the formula... 

Efficiency= Workout/Workin 

 Finally... 

Part Nine: Driving Past a Wreck at a four way stop  

  In Florida, it is common to see car crashes. When I see one or the results of one, I think of the physics concept of conservation of momentum. The symbol for momentum is P.  The formal to calculate a systems momentum is... ( M is the mass, V is the velocity, A stand for one object, B stand for the other object)

 P Total Before = P Total After 

    PA + PB = PA + PB 

- If the objects are not originally stuck together, but are afterwards you'd follow those formulas with the formula 

(MA)(VA) + (MB)(VB) = (MA+B)(V x A x B) 

- If the objects aren't stuck together before or after you'd use the formula

(MA)(VA) + (MB)(VB) = (MA)(VA)+(MB)(VB) 

Here is an example of this.... 

  Let's say I see two trucks driving towards each other, one from the north and one from the south. Both have a mass of 2000kg and moving at a speed of  50m/s. When they collide and stick together,  at what speed does the wreckage move? 

The speed is 50 m/s. 

Part Ten: Arriving home and mom says, " Let there be light!" 

  I cannot count the amount of times light bulbs have gone out. I never once even considered why only one goes out but the others stay light. I also never even thought about why when lighting strikes, all of our appliances plugged into the wall stop working. I knew a fuse had something to do with it, but I never knew what it did nor how. 

It turns out that all houses are wired with parallel circuits.... 

  In a parallel circuit, if one bulb or appliance stops working, the other appliances or bulbs are not affected. In a parallel circuit, when appliances are added the total resistance decreases, current increases, and the brightness stays the same. This is amazing compared to a series circuit, which looks like this...

  If our houses were wired with a series circuit, if only bulb or appliance stopped working, then the other appliances would all shut off. In a series circuit, if appliances are added the total resistance increases, current decreases, brightness decreases.

  Now that you understand that, I can explain fuses. A fuse is a safety device with a strip of wire inside of it that melts and breaks the electric circuit if the current exceeds a safe level. Now fuses are only added to parallel circuits, but are wired in a series compared to that circuit. Here is what that would look like ....

  Being wired in a series compared to that circuit means that when the fuse wire breaks, it'll cut the current to all of your devices to prevent a fire from breaking out.

Model Wind Turbine

Wind Turbine Model
By Layton Oliveria, Kennedy Wesley, and Katherine Santora 

Section 1: Background (How They Apply to the Wind Turbine Model) 

Primary Physics Concepts to know

1.) Electromagnetic Induction: It is the act of inducing voltage by changing the magnetic field in loops of wire. You take a loop of current carrying wire, in which when a magnet (going through, above, or near)  will change the b (magnetic field) of the loop of wire, which will induce a voltage that can change the current. This current is used for a variety of things.  We use this concept in our generator.

2.) Torque: Torque causes rotation. The two things torque requires is a force and lever arm. The Formula to find a torque is Force x Lever Arm. A lever arm is the distance from the axis of rotation to where the force is applied. The lever arms were our blades which were attached to the rod that was the axis of rotation. The force applied by the wind to the blades got the blades to spin. 

3.)  Friction: There are two things that affect fraction. The first is the nature of the the surfaces (this has nothing to do with speed or surface area) meaning rough or smooth. The second is how hard the surfaces are pushed together.  This applied to our turbine in that, the inside of the box had a rough surface area. This means that it was harder for the the brass rod to spin inside of the rough surface. The amount of friction was increased by the heavy weight of the magnets, which pushed the brass rod harder against the hole in the box. Lastly, we also experienced friction when the blades were farther from the center of mass. The blades being farther from the generator box pulled the brass rod forward. In turn, the magnets were pulled against the inside of the generator box. Since the surface of the box is rough, it'd created some friction that slowed the velocity of our wind turbine model. 

4.) Newton's Laws

- Newton's First Law:  Newton's First Law states (the Law of Inertia) ," an object at rest or an object in motion will remain at rest or in motion at the same speed in the same direction, until acted upon by an outside force." Basically, the blades of the wind turbine will remain at rest until acted upon by the outside force of the wind. Once they are acted upon, they will continue to be in motion until acted upon by an outside force such as friction. 

- Newton's Second Law: In word form, Newton's Second Law states that, "Force is directly proportional to acceleration, mass is inversely proportional to acceleration." In symbols that would be written as a=f/m. This applies to our wind turbine in that the greater the force of the wind is, the greater the acceleration of the blades will be. In addition, the greater the mass of our wind turbine, the lower the acceleration will be. 

- Newton's Third Law: Newton's 3rd Law states that, "for every action there is an equal and opposite reaction." In our wind turbine, the wind pushes the blades ---> the blades pull the wheel --> the wheel pushes the brass rod --> the brass rod pulls the magnets. These are action reaction pairs. 

5.)  Rotational Inertia and Tangential Velocity 

- Tangential/Rotational Velocity: The number of rotations or revolutions per unit of time. This is directly proportional to the tangential velocity. Tangential velocity depends on the radial distance from the axis of rotation. This applies to our turbine in that the longer the blades are, the farther they are from the axis of rotation. The farther away they are, the lower the tangential velocity will be. The larger the wheel/blades are the lower the number of the RPM's (rotations per minute) will be. 

Section 2: Materials and Methods

Materials Needed

-  6 PVC Pipes + 4 PVC elbows + 3 triple sided  PVC connectors

- 2 Rubber Washers (can differ in size depending upon the size of the hole you cut)

- 4 (2 inch) rectangular magnets

- 1 Brass rod

- 1 (2D) Circle of Basswood

- 1 Empty (2 Liter ) Plastic Bottle

- 10 (4 inch) Wooden Dowels

- 10 (4 inch) strips of cardboard

- 10 (2 inch) strips of cardboard

- 1 tube of Hobby glue (like Krazy glue)

- 1 cardboard box

-  Copper Wire

- Electrical tape

- 1 Wooden Button

Methods 

A.) The Magnet Placement 

Step one: We took two magnets and faced them so that their opposite poles would on top of one another and their magnetic filed lines would pull two magnets towards each other. Then we glued two pieces of cardboard (1/2 inch. in size) to those two magnets. Then we glued the brass rod to magnet set A. Afterwards we glued two pieces of cardboard on top of magnet set B. Then we brought aligned the opposite poles of magnet set A to magnet set B, which then stuck together since opposite poles attract and pull each other towards one another.



B.)  Coils

Step two: After glueing the box closed, we grabbed copper wire because it is a good conductor of current. We wrapped the wire twenty- one times around each side of the box. It is crucial that you make sure the wire is perpendicular to the moving magnets. Otherwise, the current carrying wire will not feel a change in the magnetic field because it'd be parallel. Then we connected the two coils and scrapped the top of both ends of each of the coils. It is important that you scrape the same side of each wire, otherwise there will be current flowing one way and right back again, and the blades would not move. We twisted one end from each coil together in the front and wrapped electrical tape around them to ensure they wouldn't come apart. We did the same process on the back, but without the electrical tape so that we could connect them to the machine that'd test the amount of current we generate.

C.) Wind Catching Device 

 View A 

Step three: We the two liter plastic bottle and cut the sides into five pieces. Then we tool four inch strips of cardboard and used the krazy glue to stick two strips on the back of each piece of plastic. We took the four inch dowels and glued them to the back of the four inch strips of cardboard. We then took two inch pieces of cardboard and glued them, using the krazy glue, to the wooden circle. We the used the crazy glue to glue the dowels attached to the plastic blades, to the circle of wood.


View B 

Step four: Then we used one of the drill bits to physical make the hole. Then we filled the hole with the crazy glue and stuck it onto the brass rod. Depending upon the glue you use, the amount of time you will have to hold and apply pressure will differ.  We then glued cardboard to the base of the PVC pipe that is vertical. Then we grabbed velcrostripes, attached one to the bottom of the box and one to the cardboard that was glued to the pipe. We then stuck those together.

D.) Overall Wind Turbine 

Section 3: Results 

How much voltage and/or current did you generate?

- We generated 0.002 A of current.

Were you able to light a lightbulb? Why or why not?

- We were not because you'd need 0.03A to light a lightbulb.

Video of Our Wind Turbine 

Section 4: Discussion 

The Factors that Influenced the Amount of Voltage Induced 


1.) The shape of the blades: Depending upon the shape, they can will harness more of the wind that'll turn the blades faster. In turn, it would turn the magnets faster. The faster the magnets move the more voltage that'll be induced.

2.) The length of the wire: The longer the wire is, the more resistance it'll have. This is because of ohm's law which states that, " I= V/R." So the greater the resistance, the lower current.

3.) The weight of the magnets: The heavier the magnet is, the greater the force of the wind would have to be. The heavier the magnets are, the slower they will spin. The slower they spin, they will cause less of a change in the magnetic field in the loops of wire. This means less current will be generated.

What Worked

- Using the strips of cardboard to connect the dowels to the blades and to the circle of wood, which made it easier to stick to the plastic and the flat circle of wood.

- Using a button with a hand drilled hole to connect the dowel to the circle of wood, which made it sturdy.

- Using rubber washers to reduce the friction between the brass rod and the cardboard box.

- Using PVC as our base, which made it sturdier.

- Using the velcro, which allowed us to take off the generator to make adjustments if needed.

- Using a box as our generator, allowed us to easily wrap the wire and have it keep its shape.

- Pulling the end of the brass dowel with the blades, closer to the generator. This brought it closer to the center of mass. 

What Didn't Work 

- Using a horizontal instead of a vertical wind turbine design. The horizontal design work best for winds at a higher elevation. The fans on the tables blew wind at a lower elevation. This made our design barely turn, since we were expecting the elevation of the fan to be greater.

- Using big rectangular magnets because the weight was just too heavy in comparison to the force of the wind. This made it harder for the wind, that the blades did harness, to turn the brass dowel.

The Various Things We Tried (that didn't work)

- We tried to use a wooden dowel, but switched to a brass dowel. This was because the wooden was heaver than the thin brass dowel. The downside was that the Brass dowel bent easier than the wooden one.

- We tried to use plastic folders from Ingles as the blades, but they were too thin and flimsy. When we put them in front of a fan, they just bent straight back.

- We tried to attach lug nuts to the end of three inch wooden dowels that would've connected to the large wooden dowel. This made it very heavy (hard to turn and stay straight). We tried to use duct tape and straws in between the dowels, but they just got heavier. In addition, they didn't properly support the small dowels.

- We tried to use the small magnets on our brass dowel, but when the number of magnet pairs were even then there was an even number of north and south poles. Therefore, they just stuck together despite the large amount of glue.  

Advice/Tips 

1.)  Use a vertical design for the wind turbine because the fan is low to the table, so the vertical turbine would be able to harness more wind.

2.) Use  the small and light magnets Mrs. Lawrence provides. They are lighter and will cause less problems.

3.) If you want a sturdy base, use PVC pipes.

4.) If you want to stick two round (3D) objects together, then glue a piece of cardboard between them.

5. ) When using hobby or Krazy glue, less is more! Plus, read the directions.

6.) You want the blades to be light, use a plastic bottle.

7.) Focus on your generator box before you start anything else. Despite what you may think, the generator is the most important part. The blades are easy to adjust, the generator not as well.


What I'd Do Differently 

- Use a vertical design

- Use the small magnets provided

- Use a bottle with slits in the side that are pulled out

Unit 7 Summary

Welcome back my fantastic physicists, you know the drill...  

1.)  Magnetism; Magnetic Poles;Electromagnetism 

2.) Forces on Charged Particles in an Electric Field; Motors 

3.) Electromagnetic Induction and Common Appliances 

4.) Generators and Energy Production 

5.) Transformers and Energy Transfer from Power Company to Home  

Part One: Magnetism; Magnetic Poles; Electromagnetism 

What is a domain?

- A domain is a cluster of electrons all spinning in the same direction.

What is the difference between the domains being aligned versus unaligned?

- Aligned domains have a magnetic field, while the unaligned do not.

What direction do the field lines run inside a magnet?

 - Inside of a magnet, the field lines run from the south pole to the north pole.

What direction do the field lines run on the outside of a magnet?

- Outside a magnet, the field lines run from the north pole to the south pole.

What is the source of all magnetism?

- The source of all magnetism is moving charges.

What is the shape of the magnetic field around the magnet?

- It is actually the shape of a cloud, it's 3D.

Draw a magnet with the field lines.

TADA!

What is the difference between North and South versus the Globe's North and South?

- The north on our globe is actually magnetic south, while our globe's south is actually magnetic north.

What is a compass?

- A compass is a magnet that is free to move.

How does a compass show the direction of the magnetic field?

- It aligns with the direction of the earth's magnetic field.

How is the magnetic field around a wire different? 

- It is similar to a sphere. However, depending upon the direction of the current, the direction will go from back to front or front to back. 


Examples and Practice Problems 

1.) Explain why a paper clip sticks to a magnet? (Use pictures to aid your explanation)

- The domains (clusters of electrons that are all spinning in the same direction) of the paper clip are randomly aligned.

- When the permanent magnet is brought near the paperclip the domains are aligned, meaning the paperclip now has a magnetic field. This means that the paperclip is now a magnet that has a north and a south pole. The paperclip's north and south poles are attracted to the opposite poles in the permanent magnet, thus it sticks to the magnet.

2.) What will happen when the paper clip is removed? If the middle paper clip is removed? Why?

Since they are now magnets, they will continue to be magnets, even if they are detached from the original permanent magnet. 

4.) Both sides of a permanent magnet can pick up a paper clip. Which is greater, the force from the magnet on the paper clip or the force from the paper clip on the magnet?

- According to Newton's Third Law that states, " for every action there is an equal and opposite reaction," the forces are equal.

5.) Draw and explain why opposite poles attract each other and like poles repel each other?

                                        

- Opposite Poles: The field lines are pointing in opposite directions, pushing the magnets away from each other. 

- Like Poles: The field lines are pointing in the same direction, attracting (pulling) the magnets towards each other.

Part Two: Forces on Charged Particles in an Electric Field; Motors 

What are the two essential parts of a motor?

- The current carrying wire and the magnet.

What is the fundamental reason a motor works?

- A current carrying wire feels a force in the magnetic field. This force causes a torque, which causes the current carrying wire to spin.

When trying to find the direction of the force exerted by the magnetic field on a current carrying wire, you use the right hand rule. Explain what three fingers you use and what they stand for.

- Thumb= Force

- Index Finger= Current

- Middle Finger= Magnetic Field

What is the specific way you scrape an armature and why?

- You either scrape just the top or just the bottom of both ends of the current carrying wire. This is because then the current will flow in one direction, pushing the wire away from us. If current is flowing on both the top and bottom of both ends of the current carrying wire then the wire will be pushed away from us, but immediately return back to the original position.


Examples and Practice Problems 

1.) Why do cosmic rays enter at the poles and not at the equator? What phenomenon is produced by cosmic rays entering the earth?

- When moving charges are perpendicular to the magnetic field, the charges feel force. At the poles, the  moving charges are parallel to the magnetic field lines so they don't feel a force and can enter the atmosphere. When at the equator, the moving charges are perpendicular to the magnetic field so they feel a force and are deflected back into space.

2.) A wire in a current is running toward the left of this page. It is in a magnetic field that is running up to the top of this page. Which way will the wire be forced? (Up, down, left, right, in, or out of the page)

- The wire will be forced into the page. 

3.) Use the diagram below for the following questions

A.) Draw the current through the loop of wire and the magnetic field on top of the magnet

-Red = Magnetic Field

-Blue = Current


C.) What will supply the current to the wire?

- The battery will supply the current to the wire.

4.) If you were to add some fan blades to the wire that this motor will spin, where would you add them? How would the motor make the fan blades spin?

- You would add them to the the ends of the loops of the current carrying wire. The current carrying wire when near a magnet feels a force. This force causes a torque, which causes the current carrying wire to spin. If the blades are attached to the wire then when the torque causes the wire to spin, the fan blades will spin. 

5.) Below are two position of the loop. The bottom one has been rotated. Use the right hand rule to show the direct that the slope will be forced. Note: only of these situations will actually produce a torque on the loop. One of these situation will just cause the loop to move to the side and the other will actually cause it to spin.

- According to the right hand rule, the loop will be pushed in.

Part Three: Electromagnetic Induction 

What is electromagnetic induction?

-It is the act of inducing voltage by changing the magnetic field in loops of wire.

How does electromagnetic induction work?

-You have a loop of wire in which when a magnet (going through, above, or near) will change the b (magnetic field) of the loop of wire, which will induce a voltage that causes a current. This current is used for a variety of things....

Examples: metal detector at an airport, credit card machines, and traffic lights.

What is Farraday's Law?

-The voltage induced is directly proportional to the number of loops.

What are the three ways to induce voltage in a loop of wire?

-The first is to move the loop near the magnet. The second is to move the magnet near the loop. The third is to change the current in a nearby loop.

Examples and Practice Problems 

1.) Why does a traffic light at an intersection change when a car approaches it?

- The traffic light at an intersection changes when a car approaches because of electromagnetic induction. In the concrete, there are loops of wire that when the car rolls over,  creates a change in the b that induces a v that causes a current. This current sends a signal to the lights to change.

Part Four: Generators and Energy Production 

What is a generator?

- A rotating coil in a stationary magnetic field.

Does a magnet moving in a loop of wire create or induce voltage? 

- It induces a voltage. 

How does a generator differ from a motor?

- The roles of input and output are reversed. In a motor, the electric energy is the input and mechanical energy is the output. In a generator, mechanical energy is the input and electric energy is the output.

What type of energy do generators convert and what is it converted into?

-They convert mechanical energy into electrical energy. 

What is the underlying principle that both a motor and a generator operate according to?

-Another way to word it from the earlier section, is that moving electrons experience a force that is a moving perpendicular to both their velocity and the magnetic field they traverse.

What is the motor effect? (see picture)

- When charge move along the wire, there is a perpendicular upward force on the charge. Since there isn't a conducting path upwards, the force on the charge pulls the wire upward.

What is the Generator effect? (see picture)

- It is when a wire with no initial current is moved downward, the charge in the wire experiences a deflecting force perpendicular to its motion. Since there is a conducting path in this direction, the charge moves, conducting a current.

Examples and Practice Problems 

1.) "A length of wire is bent into a closed loop and a magnet is plugged into it, inducing a voltage and consequently, a current in the wire. A second length of wire, twice as long, is bent into two loops of wire, and a magnet is similarly plugged into it. Twice the voltage is induced, but the current is the same as that produced in the single loop. Why? " (Chapter 25 Conceptual Physics)

- According to Farraday's Law, "the number of loops/turns is directly proportional to the voltage induced." This means that the second wire will more loops will have a greater voltage, a greater voltage in this instance means less current. This is because in generators, the power must remain the same, Power Primary = Power Secondary. Therefore, as the voltage increases the current must decrease to compensate. According to Ohm's Law, " I = V/ R," meaning current and resistance are indirectly proportional. This means as current decreases, the resistance will increase. That is why the current remains the same.  



Part Five: Transformers and Energy Transfer from Power Company to Home  

What are the two types of transformers? What is the difference between them?

- The two types of transformers are Step-Up and Step- Down. The difference between them is that in the Step-Up transformer, the primary coil will have less loops/turns than the secondary while the Step-Down's primary coil will have more loops/turns than its secondary. 

Why is power sent at such high voltages in power lines from the power company to your house? 

Power is sent at such high voltages so they can have low current.

Do transformers rely on AC (alternating current) or DC (direct current)? 

- Transformers rely on AC current. 

Why can a hum usually be hear when a transformer is operating? 

- A hum can usually be heard because the current running back and forth in the wire and is vibrating the air around it and all sound is just vibrations. 

What is the formula for finding the power of the primary versus the secondary coil? 

Primary Power = Power Secondary 
                       IV = IV  

What is the formula for finding the number of loops/turns of a coil? 

Why do you want the current in power lines to be low? 

- You want the current to be low in power lines otherwise you'd lose energy to heat if it was high. 
Examples and Practice Problems

1.) Why does a transformer rely on alternating current? In you answer, talk about what a transformer is, one place we would find one, and how it works.

- The primary coil relies on AC (alternating current) meaning the b is always changing. This causes the b of the secondary coil to change which induces a v that causes an I. A transformer is a device that increases or decreases the voltage going into a device. They can be found in appliances that need more or less voltage than the wall supplies. A transformer consists of two coils of wire, a primary and a secondary. The types types of transformers are step up and step down. In a step up transformer, the primary coil will have less loops/turns than the secondary. In a step down transformer, the primary coil will have more loops/turns than the secondary. This is in accordance to Faraday's Law which states" the number of loops is directly proportional to the voltage induced."

2.) A transformer is used to connect a computer to a wall socket. The computer requires 40V and the wall socket provides 140 V.

A.) what type of transformer is required?

- A Step-Down transformer is required.

B.) If the primary coil has 80 turns, how many will the secondary have?

- The secondary will have 22.85 loops/turns. 

C.) You go to a friend's house and they have a computer has 20V and runs on a 2A current, what will the current drawn from the wall socket, which has 120V, be?

3.) " Your friend says that according to ohm's law, high voltage produces high current. Then your friend asks, " So how can power be transmitted at a high voltage and low current in a power line?" What is your response" ( Chapter 25, Conceptual Physics)

- Power can be transmitted at a high voltage, but a low current because the power must remain equal in the primary and secondary coils. This means that if the voltage is high, then the current must compensate for the voltage's increase by decreasing. 

4.) How does the current in the secondary coil of a transformer compare with the current in the primary when the secondary voltage is twice the primary voltage?

- The secondary coil's current is half the current of the primary coil's. 

5.) " In what sense can a transformer be considered an electrical lever? What does it multiply? What does it not multiply?" (Chapter 25 Conceptual Physics)

- It can be considered an electrical lever in the sense that...

 -Work in = Work out and F in x d in = F out x d out

 - Power of Primary= Power of Secondary  and  I x V =I x V

- It multiplies the voltage and it doesn't multiply the energy.

6.) Two separate but similar coils of wire are mounted close to each other, as shown below. The first coil is connected to a battery and has a direct current flowing through it. The second coil is connected to a galvanometer.

a.) How does the Galvanometer respond when the switch in the first circuit is closed?

It changes.

b.) After being closed, how does the meter respond when the current is steady?

It doesn't move.

c.) How does the meter respond when the switch is opened?

It changes.

AKA: When you turn a DC current on and off you can induce a voltage in a secondary, but when it is running you cannot.