Activity 12: Magnetism

In this activity you will use a bar magnet to investigate the Lorenz force and induced current.

Before You Start:
Answer the following questions to the best of your ability before doing the experiment.
Sketch the magnetic field lines above the bar magnet shown above.
Which way would a proton need to move (above the magnet) to experience a magnetic force directed toward the bottom of the page?
Which way would an electron need to move (above the magnet) to experience a magnetic force directed toward the bottom of the page?
After you have thought about your answers, compare notes with your group members. Does everyone have the same predictions, or are there differing opinions?

Magnetic Force

1. Suppose you had a stream of electrons moving from left to right. In what direction would a magnetic field point if the magnetic force on the electrons was downward (toward the bottom of the page)? Justify your answer (e.g., by saying which direction which finger would point in to apply the right-hand rule.)

2. Describe how you would orient a bar magnet under (closer to the bottom of the page) the stream of electrons to accomplish this downward magnetic force.

3. How would you orient the bar magnet (and where would you locate it) to deflect the electrons into the page?

4. Go up to the demonstration at the front of the classroom and check your answers.

5. In your own words, explain how this force could increase the resistance of current flowing in a wire.

STOP. Your instructor will discuss your answers with the class before continuing.

Magnetic Data

6. Sketch the magnetic field of the two bar magnets shown above.

7. Does this combination represent a 1 or a 0?

8. Consider only the VERTICAL component of the magnetic field, which should point upwards at the north pole of the magnet and downwards at the south pole. Divide your sketch into regions in which this vertical component is increasing (becoming more up or less down) or decreasing (becoming less up or more down).

9. How many changes of "region" do you see? i.e., how many times does the change in field change direction?

10. Repeat questions 6-9 for the two bar magnets shown below.

Raise your hand for assistance. Your instructor will explain how to do the next section.

Induced EMF

Your instructor will show you how to take data for this next section. You will need to run LoggerPro and use an ULI, two bar magnets, a coil, and an amplifier plugged into Din 1 of the ULI. Make sure the amplifier is set to +/- and to HI.

11.	Set the bar magnets in the SN SN configuration from Questions 6-9. Click on Collect (or hit Enter on your keyboard) and practice taking data in this configuration. Sketch your best graph (with at least 3 passes over the magnets, preferably similar in structure).
12.	How many "peaks" are there in each data region? How does this compare to your answer to question 9?
13.	Now turn around the second magnet to obtain the SN NS configuration from Question 10. Take data in this configuration until you are satisfied with the consistency and correctness of your results. Sketch your best graph (with at least 3 passes over the magnets, preferably similar in structure).
14.	How many "peaks" are there in each data region? How does this compare to your answer to the last part of question 10?
15.	If this setup were used to read data, what data does the signal below represent?

You will be asked to complete an evaluation of today's activity and lecture before the end of class. This evaluation counts as a free 5% of each activity grade. It will generally be done on WebCT in the last 5-10 minutes of class, but time constraints may lead to the occasional evaluation done on paper.

1.	Suppose you had a stream of electrons moving from left to right. In what direction would a magnetic field point if the magnetic force on the electrons was downward (toward the bottom of the page)? Justify your answer (e.g., by saying which direction which finger would point in to apply the right-hand rule.)
2.	Describe how you would orient a bar magnet under (closer to the bottom of the page) the stream of electrons to accomplish this downward magnetic force.
3.	How would you orient the bar magnet (and where would you locate it) to deflect the electrons into the page?
4.	Go up to the demonstration at the front of the classroom and check your answers.
5.	In your own words, explain how this force could increase the resistance of current flowing in a wire.

6.	Sketch the magnetic field of the two bar magnets shown above.
7.	Does this combination represent a 1 or a 0?
8.	Consider only the VERTICAL component of the magnetic field, which should point upwards at the north pole of the magnet and downwards at the south pole. Divide your sketch into regions in which this vertical component is increasing (becoming more up or less down) or decreasing (becoming less up or more down).
9.	How many changes of "region" do you see? i.e., how many times does the change in field change direction?
10.	Repeat questions 6-9 for the two bar magnets shown below.