CH22_Inductance

=Chapter 22: Induced Voltage and Inductance= toc

1.
Complete Ch 22 Guiding Questions, #1-3, __//on your individual wiki//__. Use whatever sources you like, but make sure you credit them properly. (due 12/5)

1. What happens when you move a magnet near a coil of wire?
 * The coil induces a current (Emf)

2. What happens when you hold the magnet stationary near a coil of wire?
 * No current is induced

3. When is //emf// induced? (3 situations)
 * change angle
 * change area
 * change magnetic field strength B

2. Notes on induced emf and magnetic flux (22.1 & 22.3). Practice on Kovalcin #127 //In class 12/5//

//3.// //Demo:// Induction-- Magnet in a Coil //In class 12/5//

4. Complete Ch 22 #3, 5, 46 //in HW Journal//. (due 12/6)

5.
Do AP Problem #4. (due 12/6)

6. Complete Virtual Lab: Electromagnetic Induction Guidesheet with Lab Analysis and Conclusion. (due 12/7)

__**Virtual Lab**__
__**Electromagnetic Induction Guidesheet with Lab Analysis and Conclusion.**__

__Objective:__ Detect an induced current using a voltage meter in order to summarize the relationship between the magnetic field of a magnet and the current induced in a conductor.

__Hypothesis:__ In order to create an induced current we need a magnet and a magnetic field. We can create this current by causing a change in the magnetic flux if we rotate the coil, generating an Emf current. We know that we can do this with the equation Ø m = A*B*cosø and the equation //E// mf = ∆Ø m /∆T. As we change the angle of the magnetic flux we change its value, creating an electrical current //E// mf.

__Procedure:__

1. You can find the virtual lab at [].

2. On the left side of the screen scroll down and click on the Electricity, Magnets & Circuits link. Click on the virtual lab called “Faraday’s Electromagnetic Lab.” It should automatically download and open on your computer.

3. Prepare an observation table. You need two wide columns, labeled //Experiment// and //Observation//. For each part of the lab you will write a brief description of what you do in each step under //Experiment//. In the //Observation// column, record your observations.


 * 1) ** Induction With a Permanent Magnet ** : Click on tab called //Pickup Coil//.
 * In the middle of the right side of the screen click on voltage meter to switch the indicator on the coils from a light bulb to a voltage meter. Also click on the button that displays all charges.


 * Click and drag the coil over the north pole of the magnet. Observe the voltage meter and the green dots that represent electrons in the coil.


 * Repeat moving the coil more slowly. Observe the voltage meter. Record your observations in your Observation Table.


 * Repeat Steps b and c, moving the coil over the south pole of the magnet. Observe the voltage meter.


 * Now click on the magnet. Quickly move the north pole of the magnet in and out of the coil. Repeat slowly. Move the magnet to the other side of the coil and repeat this step using the south pole. Observe the meter.


 * 1) ** Induction With an Electromagnet: ** Click on tab called //Transformer//.
 * In the middle of the right side of the screen click on voltage meter to switch the indicator on the coils from a light bulb to a voltage meter. Also click on the button that displays all charges.


 * Move the smaller coil inside the larger coil. Observe the voltmeter and the green dots that represent electrons in the larger coil. Record your observations in your Observation Table.


 * Decrease the current in the smaller coil, by moving the slider on the battery to the left until it reads 5 V. Repeat Step b.


 * Reverse the current in the smaller coil, by moving the slider on the battery all the way to the left. Repeat Step b.


 * Replace the DC battery with AC power supply, by clicking on the AC button in the box labeled Current Source on the top right side of the screen. Repeat Step b.


 * Increase the magnitude of the power supply by moving the slider on the left side of the power supply up. Repeat Step b.

__Data:__ voltage meter and the green dots that represent electrons in the coil. || The needle of the voltmeter moves towards the negative end of the spectrum. The electrons move as the coil does with the current going into the negative end of the voltmeter. || your observations in your Observation Table. || The needle barely moves at all towards the negative end, and the electrons flow through the circuit, but very slowly. || Observe the voltage meter. || The voltmeter does the same thing as in the north pole, but the needle bends towards the positive end. The electrons also go in the opposite direction as at the north pole of the magnet. || slowly. Move the magnet to the other side of the coil and repeat this step using the south pole. Observe the meter. || The same thing happens as in the three steps above. || dots that represent electrons in the larger coil. || Similarly to the magnet from the first experiment, the electrons of the voltmeter's coil moves only when the smaller coil is moving. In this experiment, however, the voltmeter reads a charge to the negative end when the smaller coil enters from either side. || battery to the left until it reads 5 V. Repeat Step b. || The voltmeter has a lower reading of induced current, and there are less electrons in the larger coil. || all the way to the left. Repeat Step b. || This is the same as initially when the battery was at 10V in the other direction, but the current of the larger coil is going in the opposite direction, and the voltmeter reads a positive value. || the box labeled Current Source on the top right side of the screen. Repeat Step b. || Now the reading in the voltmeter, as well as the induced current in the larger coil, are alternating. This is because the current of the power supply changes, and the induced current changes with it. So some times the induced current will be positive and sometimes it will be negative. || side of the power supply up. Repeat Step b. || Now the induced current is going much faster than before, and the voltmeter is getting larger readings than in the previous experiment. || __Discussion Questions:__
 * Experiment || Observation ||
 * Click and drag the coil over the north pole of the magnet. Observe the
 * Repeat moving the coil more slowly. Observe the voltage meter. Record
 * Repeat Steps b and c, moving the coil over the south pole of the magnet.
 * Quickly move the north pole of the magnet in and out of the coil. Repeat
 * Move the smaller coil inside the larger coil. Observe the voltmeter and the green
 * Decrease the current in the smaller coil, by moving the slider on the
 * Reverse the current in the smaller coil, by moving the slider on the battery
 * Replace the DC battery with AC power supply, by clicking on the AC button in
 * Increase the magnitude of the power supply by moving the slider on the left

1. Based on your observations from the first part of the lab, did the speed of the motion have any effect on the galvanometer?
 * Yes, the speed of the magnet going through the coil determined the magnitude of the induced current. As the magnet moved faster through the coil, the voltmeter got a larger reading of current in magnitude, and the induced current was moving faster.

2. In the first part of the lab, did it make any difference whether the coil or the magnet moved?
 * No, the readings on the voltmeter were the same regardless of whether the magnet or coil were doing the moving to induce the current.

3. Explain what the voltage meter readings revealed to you about the magnet and the wire coil.
 * The voltage meter readings told us the relative direction of the induced current flow, as well as the relative magnitude. As the induced current got larger or smaller, or if it reversed directions, we were able to tell from the voltmeter.

4. Based on your observations, what conditions are required to induce a current in a circuit?
 * To induce a current we need a magnetic field, a circuit with current in it, and a circuit with no current going through it. The circuit with current will induce a current in the circuit without a current.

5. Based on your observations, what factors influence the direction and magnitude of the induced current?
 * The magnitude of the induced current is dependent on the speed in which the initial current passes through or past the circuit without current, as well as the magnitude of the current in the powered circuit.

__Conclusion:__

Based on the observations from the online experiment we are able to correct the hypothesis and make it more accurate. We were correct in saying that a current is induced by changing the magnetic flux Ø m, and that this could be done by changing the angle. We discovered through experimenting that the rate at which the angle changes also affects the induced current, which makes sense according to the equation //E// mf = ∆Ø m /∆T. To induce a current, we need a magnetic field, something to induce the current (a magnet or a circuit with a current going through it), and a circuit with no current going through it. We also know now that the magnitude of the induced current depends on the magnitude of the original current, as well as how fast the circuit passes the circuit without a current. The direction of flow of the induced current can also be seen, and is dependent on the direction in which the inducer passes the circuit that has no current. The direction of flow of an induced circuit, when induced by a power supply, is also dependent on the direction in which the original current flows.

7. Complete Ch 22 Guiding Questions, #4-8, __//on your individual wiki//__. Use whatever sources you like, but make sure you credit them properly. (due 12/7)

4. What is Faraday's law of induction?
 * Emf can be induced in a loop if the magnetic flux is changing. The rate of change is the major influence on the amount of induced Emf. E=(-N * )/(t)

5. Why is the expression for Faraday’s Law negative?
 * it comes from Lenz' Law

6. What is Lenz’s Law?
 * The induced Emf generates a current that sets up its own magnetic field. This magnetic field acts to oppose the change in flux. A magnetic field that is induced will always try to maintain the status quo.

a) If nothing is changed, what is the induced emf? b) The magnetic field is increased uniformly from 0.3 T to 0.8 T in 1.0 seconds. While the change is taking place, what is the induced emf in the coil? c) While the magnetic field is changing, the emf induced in the coil causes a current to flow. Does the current flow clockwise or counter-clockwise around the coil?
 * //7. Consider a flat square coil with N = 5 loops. The coil is 20 cm on each side, and has a magnetic field of 0.3 T passing through it. The plane of the coil is perpendicular to the magnetic field: the field points out of the page.//**
 * the Emf = 0 because nothing changes to induce the current at all.
 * E = n*(flux)/t
 * E = 5 * 0.5 * 0.04/1
 * E = 0.1V
 * B p = out
 * increase
 * Flux p = out
 * Flux s = in
 * B s = in With our knowledge of the right hand rule we know the current is moving clockwise.

8. Check out: [|**http://micro.magnet.fsu.edu/electromag/java/lenzlaw/index.html**]. Record your observations.

8. OPTIONAL Gizmo: Magnetic Induction. Go to gizmo and click on "Lesson Materials", and either print or download the guidesheet needed to complete the Gizmo. Don't forget to do the 5 Online Assessment questions when you are done. (due 12/9)

9. Notes on Faraday’s Law and Lenz’s Law (22.4&22.5). Practice Kovalcin #128. //In class 12/7//

10.
Do Activity: Lenz’s Law //In class 12/7//

11. Complete Prelab questions for Solenoid Lab __//on your individual wiki//__. (due 12/8)

1. What is your hypothesis? Include the rationale for your hypothesis. How do you think you might test this hypothesis?

The magnetic field strength of a solenoid is going to be calculated with the equations B = (µ o )* // I // * n ( n= number of coils / length of solenoid) , and in this experiment we are testing how distance affects the magnetic field strength. Because of this, we are going to keep the current and number of coils and length constant, only changing the distance the sensor is from the center of the solenoid. I believe that the magnetic field strength from a solenoid will increase on the sensor as the distance decreases, and vice versa.

2. Read the entire procedure through. Done

3. Design a data table in order to record your observations and calculations.



4a. How does the strength of the magnetic field inside a solenoid relate to the position inside? On one end of the solenoid there will be a negative magnetic force and the other will have a positive, but this is simply because the direction of current flow (from the sensors point of view) is reversed. As more of the sensor goes into the solenoid, there will be a greater magnetic field exerted on the sensor. This proves that the magnetic field has an area of greatest strength in the center, and gets weaker as we go farther away from that center.

4b. Is the magnetic field the same strength at every location within the solenoid? <span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif;">No, the magnetic field strength is not uniformly distributed and is strongest in the center.

<span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif;">4c. What is the magnitude of the magnetic field inside a very long solenoid? The magnetic field is weaker, and this is because the n in the equation is # coils / length. As length increases, the magnetic field strength decreases.

<span style="background-color: #ffffff; font-family: Arial,Helvetica,sans-serif;">4d. What is the relationship of the magnetic field strength and radius of the coil? The maximum magnetic field strength is determined by the equation B = (µ*I)/(2π*r) where r is the radius. As the radius increases, the magnetic field strength at the center decreases and vice versa.

12. LAB: Magnetic Field in a Solenoid Labsheet. Complete the Analysis and Conclusion. //In class 12/8//

13. Complete Ch 22 #9, 11, 21, 23, 25 //in HW Journal//. (due 12/9)

14. Do AP Problem #5. (due 12/9)

15.
Quiz on Chapter 22 (Part 1) //In class 12/9//

16. OPTIONAL Gizmo: Electromagnetic Induction. Go to gizmo and click on "Lesson Materials", and either print or download the guidesheet needed to complete the Gizmo. Don't forget to do the 5 Online Assessment questions when you are done. (due 12/12)

17. Complete Ch 22 Guiding Questions, #9-17, on wiki. Use whatever sources you like, but make sure you credit them properly. (due 12/9)

9. __Why__ is an //emf// induced between the ends of a rod moving in a magnetic field?
 * Because when the rod moves in the magnetic field, it causes a change in magnetic flux and as a result induces an Emf.

10. What is motional //emf//?
 * It is the result of an induced current in a magnetic field.

11. When is motional //emf// largest?
 * Emf is the largest when a coil with many loops experiences a significant change in flux in an extremely short period of time.

12. What happens if the metal rod is part of a complete circuit?
 * It will induce a current in the circuit, and the direction of the current can be found using the right hand rule.

13. Derive the equation: V = Bl//v//
 * V = (Change in flux)/(change in time) and A = l*v*t and flux = B*A
 * V = B*A/t
 * V = B*l*v*t/t
 * V = B*l*v

14. Why is an electric field produced when a conducting rod is moved in a magnetic field?
 * The rod induces a current, and this current causes the magnetic field.

15. How is the concept of motional //emf// consistent with Faraday’s Law?
 * When flux does not change there is no Emf, which is consistent with Faraday's Law's equation: E = N*(flux)/time, as it would become E = N*(0)/t = 0. When there is a change in flux, caused by a change in the magnet or magnetic field, we see a non-zero value in the equation as well.

16. The sliding bar has a length of 0.50 m and moves at 2.0 m/s in a magnetic field of magnitude 0.25 T. (a) Find the induced voltage in the moving rod. (b) If a 0.50 W resistor was placed in the circuit, what would the current be? (c) What force must be applied to the rod to keep it moving at constant speed?
 * **a.)** V= B*l*v
 * V = 0.25 * 0.5 * 2
 * V = 0.25
 * **b.)** V=I*R
 * 0.25 = (0.5)*I
 * I = 0.5A
 * **c.)** F = B*I*L
 * F = (0.25)*(0.25)*(0.25)
 * F = 0.125N

17. See animation: [] ** Record your observations. **

18. Wiki (Ch21/22) (due 12/9)

19. Discuss Chapter 22.2. Notes on Motional emf with practice on Kovalcin #128. //In class 12/9//

20.
Complete Ch22#17,19,55 //in HW Journal//. (due 12/12)

21. Do AP Problem #3 [|(due 12/12)]

22. Concept Map - //In class 12/12// E&M [|Terms]

23. Chapter 20 Concept "Test" [|Questions] //In class 12/12//

24. Do AP Problems #1,8,12. (due 12/13)

25.
True/False 70 T-F (due 12/13)

26. Chapter 21 Concept "Test" [|Questions] //In class 12/13//

27. Test on Chapters 21 and 22. //In class 12/14//

28. Hand in HW Journal. [|(due 12/14)]