LAB-9 Induction: Magnet through a Coil Page 1 of 6Written by Chuck HuntInduction: Magnet through a CoilGOALsThe purpose of this experiment is to examine Faraday’s Law of Induction. A magnet will be dropped through a coil and the voltage across the coil graphed as a function of time. The total integrated flux as the magnet moves into the coil will be compared to the flux as it moves out of the coil.TheoryWhen the magnetic flux thru a coil of wire changes (as in a magnet falling thru a coil of wire in Figure 1), there is an EMF (E) generated between the ends of the coil given by Faraday’s Law:E = -N(dΦ/dt) (1)where N is the number of turns in the coil and dΦ/dt is the time rate of change of the magnetic flux, Φ, or the derivative of the magnetic flux with respect to time. The magnetic flux may be thought of as the number of magnetic field lines (green arrows in Figure 1) passing thru the coil. Integration of Equation 1 yields:∫E dt = -NΔΦ = [the area under the curve on an E vs. t graph] (2)where ΔΦ is the total change in flux (or total number of field lines).Equipment1AC/DC Electronics LaboratoryEM-86561Voltage SensorCI-65031Bar Magnet Alnico (set of 2)EM-86201No-Bounce PadSE-7347Required but not included:1850 Universal InterfaceUI-50001PASCO Capstone SoftwareFigure 1: Falling MagnetNSLAB-9 Induction: Magnet through a Coil Page 2 of 6Written by Chuck HuntSetup1. Remove the large plastic bolt from the center of the coil. Note: replace the bolt at the end of the experiment. Otherwise the coil tends to be pulled loose from the circuit board.2. Connect white wire jumpers from the coil connector springs to the banana inputs for the Electronics Laboratory as shown in Figure 2. Connect red and black ends of the Voltage Sensor to the banana inputs on the Electronics Laboratory and plug the Voltage Sensor into Channel A on the 850 Universal Interface.Figure 2: Setup Figure 3: Paper Roll Guide3. In PASCO Capstone, set the sample rate to 2.0 kHz and create a graph of Voltage vs. time.4. Open the Recording Conditions and set a start condition for the measurement of Voltage rising above 0.01 V and set a stop condition based on a time of 0.25 seconds.5. Position the Electronics Laboratory so it hangs over the desk enough so a magnet can be dropped through the coil. Placing the iron core for the coil (or any convenient mass) in one of the battery holders will prevent the Electronics Laboratory from tipping. Alternatively, hold it with clamps, rods and stands.LAB-9 Induction: Magnet through a Coil Page 3 of 6Written by Chuck Hunt6. Place the No-Bounce pad on the floor or top table where the magnet will hit. If the magnet hits the floor without the pad, it may break or damage the floor!7. Tightly roll up a piece of paper to make a tube 8.5 inches long and insert it into the coil. This will guide the falling magnet, so it hits the hole. Mark where the magnet must be held so its lower end is about 5 cm above the coil.ProcedureNote: The PASCO EM-8620 Alnico magnet has a groove near the North end. Hold one magnet so its north end is downward and is in the paper tube about 5 cm above the coil. Check polarity with a compass!1. Click RECORD. Drop the magnet. Data collection will start and stop automatically. If you only see an “up pulse”, reverse the connections on the coil by reversing the red and black banana plugs from the voltage sensor. Repeat this step until you have clean data!2. Click open the Data Summary at the left of the page. Re-label this run as “N down”.3. Click on Recording Conditions at the bottom of the page. Change the Start Condition to “Falls Below” and the Value to -0.0100. Click OK.4. Repeat steps 1 & 2 with the south end down. Label it “S down”.5. Click on Recording Conditions at the bottom of the page. Change the Start Condition to “Rises Above” and the Value to 0.0100. Click OK.6. Repeat steps 1 & 2 with the north end down but held as high as possible in the paper tube. Label this run “N down hi”.7. Repeat steps 1 & 2 with the south end down but held as high as possible in the paper tube. Label this run “S down hi”.8. Remove the paper tube.9. Stick the two magnets together (north to south). Hold them so one end is already in the top of the coil (they will just barely fit). Repeat step 2 and label “N to S”.10. Tape the two magnets together so the north poles are together, and the south poles are together. Hold them so the north end is already in the top of the coil (they will just barely fit). Repeat step 2 and label “N to N”.11. Tape the two magnets together so the north poles are together, and the south poles are together. Hold them so the south end is already in the top of the coil (they will just barely fit). Repeat step 2 and label “S to S”.LAB-9 Induction: Magnet through a Coil Page 4 of 6Written by Chuck Hunt12. Replace the plastic bolt holding the coil to the circuit board.Analysis1. Create tables as shown below:Table I: Change in Magnetic Flux = N ΔΦ first pulseSystemTime range(s)Peak voltage(V)First Pulse(Vs)1N down2S down3N down hi4S down hi5N to S6N to N7S to STable II: Change in Magnetic Flux = N ΔΦ second pulseSystemTime range(s)Peak voltage(V)Second Pulse(Vs)1N down2S down3N down hi4S down hi5N to S6N to N7S to S2. Select the “N down” run on the graph. Click on the Scale-to-Fit icon. Click on the Properties icon in the graph toolbar. Show Run Symbols and Show Data Points should not be selected (so you can see the line better). If they are selected, de-select them in both the Active Data Appearance box and the Future Data Appearance box. Click OK.3. Click on the Selection icon in the graph toolbar. Adjust the handles on the selection box to select the data time = 0 to the point where V = 0 as the curve crosses the horizontal axis. You should have selected all the positive data.4. Click the Area icon. It will calculate the area under the curve. Recall from Theory that this is the change in the magnetic flux through the coil. If the Area box does not show three significant figures, click on Data Summary. Click on the Voltage Properties icon (not the Voltage Sensor Properties) and change to three significant figures under the Number Format. Enter the value in the First Pulse column of Table I on the N down line.LAB-9 Induction: Magnet through a Coil Page 5 of 6Written by Chuck Hunt5. Move the selection box to select all the negative data. Enter the value in the Second Pulse column of Table I.6. Repeat for the all entries in data sets.7. INCLUDE Graphs to validate table population entries for at least first pulses!WRAPING RESULTS1. On the graph, select the “N down” run. Why is the peak voltage higher on the 2nd pulse than on the 1st pulse?2. Why is one pulse up and the other pulse down?3. Explain why the value for the magnitudes of the change in magnetic flux for the “N down”, “S down”, and “N down hi” are all essentially equal. Include % differences!4. Select both the “N down” and “S down” runs. In terms of the magnetic flux, explain why they are reversed.5. Select the “N down” and “N down hi” runs. Explain why they are different. Why doesn’t this change the area under the curve?6. Select the “N down” and “N to S” data. Explain the difference. Show with both graphs to discuss answer and % differences7. Explain why the “N to N” or “S” to S” data in Table 1 and 2 are different from the other cases. Note: the two magnets probably were not equally strong. A 10% difference would not be surprising.SYNTHESYS QUESTIONS1) Based on your observations in this lab, describe the characteristics of an electric coil generator that you would optimize to get the most electromotive force out?2) You may have noticed that the second peak of the voltage curve is always in the opposite direction of the first peak. However, you may not have noticed that it is also a slightly higher peak. Can you describe why that might be?3) The emf produced from dropping a magnet through a coil is a form of energy transformation. What kind of transformation is it?A. Thermal energy is transformed into electrical energy.B. Mechanical energy is transformed into thermal energy.C. Kinetic energy is transformed into electrical energy.D. Electrical energy is transformed into thermal energyLAB-9 Induction: Magnet through a Coil Page 6 of 6Written by Chuck Hunt4) If a generator with a 200-turn coil produced 120 V of electromotive force, how much would it produce if it was upgraded to an 800-turn coil?A. 40 VB. 480 VC. 220 VD. There is not enough information to draw a conclusion.5) The equation for Faraday's Law includes a negative sign on one side. What does it represent?A. Magnetism is an inherently negative force.B. Opposites attract.C. The EMF generated seeks to reinforce the change in magnetic field.D. The EMF generated seeks to oppose the change in magnetic field.6) Fill in the blanks from the list of randomly ordered words in the Key Term Challenge Word Bank (Coil, Displacement, Faraday's, Field, Magnetic flux, Magnetic field, Motor)“ ____________ Law defines the relationship between the number of turns in a ____________ (N), and the rate of change in ____________ (Φ). The magnetic flux is related to the strength of the ______________ (B) , the area enclosed by the wire loop, and the angle between them. Because of the geometry of the experiment, we can say that the flux is proportional to the strength of the ____________.”RUBRIC:(5 pts)(4 pts)(3 pt)(2 pts)(1 pt)(0 pts)Introduction, materials, experimental design, procedureTables and GraphsWrapping ResultsSynthesis QuestionsConclusions