What happens if you move the magnet next to the coil

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Unformatted text preview: he sign of the induced potential difference the same if you hold the magnet steady and instead move the coil? How does changing the velocity of the moving magnet (or the moving coil) change the magnitude and sign of the induced potential difference? How does the sign of the induced potential difference change when you (i) push the magnet into the coil; (ii) leave it in the coil without moving, and iii) pull it out of the coil? What happens if you move the magnet next to the coil? Try it. MEASUREMENT Determine the sign of induced potential difference across the ends of the coil when you push the north pole of the magnet through the coil and when you push the south pole of the magnet through the coil. 178 THE SIGN OF THE INDUCED POTENTIAL DIFFERENCE – 1302Lab6Prob3 Repeat the measurements, but this time keep the magnet still and move the coil. CONCLUSION Did your results agree with your predictions? Explain any differences. 179 THE SIGN OF THE INDUCED POTENTIAL DIFFERENCE – 1302Lab6Prob3 180 PROBLEM #4: THE MAGNITUDE OF THE INDUCED POTENTIAL DIFFERENCE You’re part of a team designing a bicycle speedometer. It is a circuit with a small pickup coil on the bicycle’s front fork, near the wheel’s axle. When riding the bike, a tiny magnet attached to one of the spokes passes by the coil and induces a potential difference in the coil. That potential difference is read by a detector, which sends the information to the speedometer. You wonder how fast the bike must move to produce a detectable signal. You decide to model the situation by calculating how the induced potential difference across the ends of a coil of wire depends on the velocity with which a magnet is thrust through it. To check your calculation, you set up a laboratory model in which you can systematically vary the speed of the magnet by mounting it on a cart and rolling the cart down a ramp from different positions on the ramp. At the end of the ramp, the cart passes through the center of a coil of wire. Instructions: Before lab, read the laboratory in its entirety as well as the required reading in the textbook. In your lab notebook, respond to the warm up questions and derive a specific prediction for the outcome of the lab. During lab, compare your warm up responses and prediction in your group. Then, work through the exploration, measurement, analysis, and conclusion sections in sequence, keeping a record of your findings in your lab notebook. It is often useful to use Excel to perform data analysis, rather than doing it by hand. Read: Tipler & Mosca Chapter 28.2. EQUIPMENT You have a coil of 200 turns of wire, a magnet, meterstick, cart, and track. The track is raised at an incline using wooden blocks. You also have voltage probe with software called VoltageTimeLAB. Coil Magnet Cart Track Table Table Read the section Magnetizing a Bar Magnet in the Equipment appendix if you need to remagnetize your magnets. Read the section VoltageTimeLAB - MEASURING TIME-VARYING VOLTAGES in the Software appendix. If equipment is missing or broken, submit a problem report by sending an email to labhelp@physics.umn.edu. Include the room number and brief description of the problem. 181 THE MAGNITUDE OF THE INDUCED POTENTIAL DIFFERENCE – 1302Lab6Prob4 WARM UP 1. Draw a picture of the situation. Label important distances and kinematic quantities. Decide on an appropriate coordinate system and add it to your picture. 2. Use Faraday’s Law to relate change of magnetic flux to the magnitude of the induced potential difference in the coil. 3. Draw a magnetic field map of a bar magnet. Draw the coil of wire on the magnetic field map. As the bar magnet passes through the coil, when is the flux change the strongest? What is the relationship between the velocity of the bar magnet and the change of the magnetic flux through the coil? This tells you, qualitatively how the flux changes with time. 4. Look at the time rate change of the magnetic flux. How is it related to the velocity of the cart? It is important to note whether or not the quantities of interest vary with time or with the cross-sectional area of the coil. 5. What physics principles can you use to determine the velocity of the magnet as it passes through the coil to the starting position of the cart? 6. Write an equation giving the induced potential difference across the ends of the coil of wire as a function of the velocity of the magnet through the coil. 7. Write an expression for the velocity of the cart through the coil as a function of its starting distance from the coil. Substitute that into the equation for the induced emf. PREDICTION Calculate the induced potential difference in the coil as a function of the distance from the coil at which the cart is released and other quantities that are not changed. Make a graph of this function. EXPLORATION Before you begin exploring, consider what the signal displayed by the VoltagetimeLab program will look like. Will you be able to tell by the signal when the cart has not passed thro...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.

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