Faraday’s Law of Electromagnetic Induction Spring 2020, Distance Lab 4 Electromagnetic Induction INTRODUCTION In a previous experiment, we explored the idea that electric current creates a magnetic field. This week we’ll examine a similar phenomenon: if we have a changing magnetic field, we can induce a potential difference in a loop of wire, which leads to a current. In this experiment we’ll drop a magnet from different heights through loops of wire. We’ll investigate how the changing the speed at which a magnet passes through coils (by changing the drop height), the number of turns of wire in those coils, and the size of the magnet affects the induced voltage. Also – don't forget, there is a recitation due this week. Please submit it separately in Blackboard, to the appropriate assignment! Faraday’s Law of Electromagnetic Induction Spring 2020, Distance Lab 4 SIMULATION Before doing the simulation, check out the video that we posted on Blackboard. It will run through an overview, and help you get started with the simulation. Make some predictions about how you expect induction to work. We’ll revisit those as we do the simulation and the lab. QUESTION 1: SUPPOSE WE DROP A MAGNET THROUGH SOME COILS OF WIRE . IF YOU CHANGED THE FOLLOWING PARAMETERS , WHAT EFFECT DO YOU THINK IT WOULD HAVE ON THE INDUCED VOLTAGE ? EXPLAIN IN THE SPACE BELOW EACH STATEMENT . A: DOUBLING THE NUMBER OF TURNS IN THE COIL WILL __[DELETE THIS TEXT AND FILL IN HERE ]__ THE INDUCED VOLTAGE IN THE COIL . B: TRIPLING THE NUMBER OF TURNS IN THE COIL WILL __[DELETE THIS TEXT AND FILL IN HERE ]__ THE INDUCED VOLTAGE IN THE COIL . C: DOUBLING THE DROP HEIGHT WILL __[DELETE THIS TEXT AND FILL IN HERE ]__ THE __[DELETE THIS TEXT AND FILL IN HERE ]__ THE INDUCED VOLTAGE IN THE COIL . D: TRIPLING THE DROP HEIGHT WILL INDUCED VOLTAGE IN THE COIL . Ok, now let’s get to the simulation. You can access it here: https://phet.colorado.edu/en/simulation/faradays-law. Ok, on to the simulation itself! Experiment for a bit with all of the functions, see what happens when you turn the magnet around, anything you can think of. QUESTION 2: DOES THE MAGNET HAVE TO BE INSIDE EITHER OF THE COILS TO GENERATE A VOLTAGE ? WHAT SPECIFICALLY NEEDS TO HAPPEN TO LIGHT UP THE BULBS ? BE SPECIFIC , CONCISE , AND CLEAR ! Faraday’s Law of Electromagnetic Induction QUESTION 3A: COMPARE Spring 2020, Distance Lab 4 THE APPARENT MAXIMUM VOLTAGE ON THE VOLTMETER WHEN YOU MOVE THE MAGNET SLOWLY THROUGH THE TWO -LOOP COIL TO WHEN YOU MOVE THE MAGNET FASTER THROUGH THE SAME COIL . QUESTION 3B: OK, LET ’S TRY TO BE QUANTITATIVE . TRY MOVING THE MAGNET THROUGH THE 2-LOOP WIRE AT 3 DIFFERENT SPEEDS : SLOWLY , QUICKLY , AND SOMETHING IN BETWEEN . WHAT IS THE RELATIONSHIP BETWEEN THE MAGNET ’S SPEED AND THE INDUCED VOLTAGE ? DO YOU THINK IT ’S LINEAR , QUADRATIC , OR SOMETHING ELSE ? YOU CAN DO THIS! QUESTION 3C: COMPARE THE APPARENT MAXIMUM VOLTAGE ON THE VOLTMETER WHEN YOU MOVE THE MAGNET SLOWLY THROUGH THE TWO -LOOP COIL TO WHEN YOU MOVE THE MAGNET AT THE SAME SPEED THROUGH THE FOUR -LOOP COIL . Faraday’s Law of Electromagnetic Induction Spring 2020, Distance Lab 4 LAB VIDEO Check out the video for this experiment. It’s important, and you probably won’t be able to do the lab without it! https://www.youtube.com/watch?v=xjnMNA-sbdU. QUESTION 4: WHY DID WE WANT TO AVOID TRIALS WHERE THE MAGNET DID NOT FALL CLEANLY THROUGH THE LOOPS OF WIRE ? DATA ANALYSIS GUIDE The “high gain” input gives us a curve that looks like the one below for a magnet falling through a coil of wire. This particular curve is the one from the video. Faraday’s Law of Electromagnetic Induction QUESTION 5: RELATE Spring 2020, Distance Lab 4 THE SHAPE OF THIS CURVE TO THE MOTION OF THE MAGNET AS IT FALLS THROUGH THE COIL . CLEARLY LABEL OR EXPLAIN THE FOLLOWING PORTIONS OF THE GRAPH: A. MAGNET FAR AWAY , ABOVE THE COIL B. MAGNET ENTERING THE COIL C. MAGNET EXACTLY IN THE CENTER OF THE COIL D. MAGNET LEAVING THE COIL E. MAGNET FAR AWAY , BELOW THE COIL QUESTION 6: W HY DO YOU THINK THE MAGNITUDE OF THE INDUCED VOLTAGE WAS LARGER FOR THE NEGATIVE SPIKE THAN THE POSITIVE SPIKE ? Once again the lab data you need has been provided for you. This data was collected by PHS 240 students last spring. Ok, let’s study the effect that the number of coils has on the induced voltage in the coil. Make a plot of the induced voltage vs. N (where N is the number of loops in the coil) for the 28 cm drop height for each magnet (note that there are 3 different magnet sizes, so you should have 3 graphs or 1 graph with 3 lines for this part). Make sure to choose the x-y scatter plot that doesn’t add a line connecting the data points, and remember that we describe axes in the form “y vs. x”, so induced voltage goes on the vertical axis and N goes on the horizontal axis. Label them and include units as appropriate.QUESTION 6A: COPY/PASTE YOUR PLOTS BELOW AND ADD A DESCRIPTIVE CAPTION . QUESTION 6B: WHAT IS THE RELATIONSHIP BETWEEN INDUCED VOLTAGE AND THE NUMBER OF TURNS IN A COIL OF WIRE , BASED ON YOUR PLOTS ? Now choose one of the coils and make plots of induced voltage vs. drop height for each magnet (again, 3 graphs or 1 graph with 3 lines). QUESTION 7A: COPY/PASTE YOUR PLOT BELOW , AND ADD A DESCRIPTIVE CAPTION . Faraday’s Law of Electromagnetic Induction QUESTION 7B: WHAT HEIGHT ? Spring 2020, Distance Lab 4 IS THE RELATIONSHIP BETWEEN INDUCED VOLTAGE AND DROP Calculate the velocity of each magnet as it passes the center of the coil (hint: conservation of energy) for each drop height for that magnet and make three more plots of induced voltage vs. velocity. QUESTION 7C: WHAT IS THE RELATIONSHIP BETWEEN INDUCED VOLTAGE AND VELOCITY ? QUESTION 8: LOOK BACK AT YOUR PREDICTIONS IN QUESTION 1. HOW DO THOSE PREDICTIONS STACK UP NOW THAT YOU ’VE GONE THROUGH THE DATA ANALYSIS ? SUMMARY AND SUBMISSION GUIDELINES That’s it! Hope it went well. Please submit your filled-in writeup to the Assignment in Blackboard. All labs are due Thursday, April 16 at noon.
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