Magnetic Fields of a Bar Magnet and of the Earth
OBJECTIVE:
To examine the magnetic field associated with a bar magnet and construct the magnetic field lines.
INTRODUCTION :
In these exercises, you will study the magnetic field of bar magnets and the earth. You will draw field
lines.
PROCEDURE :
Part 1: Set-Up / Constructing Magnetic Field Lines of a Bar Magnet
1. Tape two pieces of white paper side-by-side to make one large paper.
2. Flip the paper over so that the tape is now on the back side.
3. Orient your page as a “landscape”.
4. Place a large bar-magnet 3 cm down from the top of your page, centered.
5. Trace the outside of the bar-magnet and indicate the North and South poles.
6. Place a small dot on the following locations of your bar-magnet tracing:
(The numbers in the parentheses refer to the locations seen in FIGURE 1)
a.
b.
c.
d.
e.
f.
midpoint of the two short legs of the bar-magnet tracing. (1 & 8)
diagonal off of the lower two corners of the bar-magnet tracing. (2 & 7)
directly below the lower two corners of the bar-magnet tracing. (3 & 3)
one cm in from the lower left corner of the bar-magnet tracing. (4)
two cm in from the lower left corner of the bar-magnet tracing. (5)
three cm in from the lower left corner of the bar-magnet tracing. (6)
SEE FIGURE 1 BELOW:
1
N
2 3
4
8
S
5
6
3 7
Figure 1 Setup for constructing magnetic field lines of a bar magnet
7. Place a compass at position 1 of the magnet and make the compass needle point directly at
the dot at that location.
8. Make another dot on the paper at the other end of the compass needle.
9. Move the compass so that the end of the needle that was next to the magnet is pointing
directly the dot you made in step # 8. NOW make a new dot at the other end of the
compass needle.
10. Continue this process until the compass comes back to the magnet or leaves the edge of the
paper.
11. Draw a line through the dots and indicate with an arrowhead the direction in which the
North end of the needle pointed, as shown below in Figure 2. Magnetic field lines should
flow out of the North ends and into the south ends of magnets.
12. Repeat for the remaining position of the magnet (2-6).
Figure 2 Constructing magnetic field lines
Part 2: Set-Up / Constructing a Magnetic Field Diagram with Two Magnets
1. Start with a piece of 11” x 17” Paper. If you don’t have any you may tape two pieces of white paper sideby-side to make one large paper. If you use two pieces of paper be sure to flip the paper over so that the
tape is now on the back side.
2. Orient your page as a “landscape”.
3. Place two magnets 13 cm apart, centered from top to bottom on the page. See Figure 3 below:
4. Label the starting positions seen in figure 3 with a small dot like you did in part 1.
a. midpoint of the short legs of the left bar-magnet tracing. (1)
b. diagonal off of the both corners of the left bar-magnet tracing. (2,3)
c. one cm in from the upper and lower corners of the left bar-magnet tracing. (4,5)
d. two cm in from the upper and lower corners of BOTH bar-magnet tracing. (6,7,10,11)
e. three cm in from the upper and lower corners of BOTH bar-magnet tracing. (8,9,12,13)
5. From these starting positions, use the compass just as you did in part 1. Stop your line when you hit
either magnet or go off the page.
Please do NOT force a north pole to touch a north pole or a south pole to touch a south
pole, as this will demagnetize the magnets.
Figure 3
8
6
N
9
7
4 2
S
1
5
3
10
12
13 cm
N
S
11
13
Part 3: How Can We “See” the Earth’s Magnetic Field?
Watch the following video and then follow the instructions below.
*The videos can also be found on the 8th grade science Wiki
http://www.youtube.com/watch?v=j8XNHlV6Qxg
1. Draw a picture of the image with the iron filings sprinkled all around.
2.
Explain why the filings on top magnet seem to point vertically upward from the magnet? The
following video may help you see this phenomena even more clearly.
http://www.youtube.com/watch?v=8llkHQtaOlg
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
3.
Answer the question in the video that begins at 1 min 39 sec regarding the bar magnet in the earth
appearing “upside down”.
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
4.
Explain why showing a bar magnet inside the Earth is a misleading representation of what is really
happening to create the Earth’s magnetic field.
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
____________________________________________________________________________________________
*http://temsscience8.wikispaces.com/GEOLOGY