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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
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
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
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
If equipment is missing or broken, submit a problem report by sending an email to
firstname.lastname@example.org. 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
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.
- Spring '14