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 markers on the following locations of your bar-magnet tracing:
1. midpoint of the two short legs of the bar-magnet tracing.
2. diagonal off of the lower two corners of the bar-magnet tracing.
3. directly below the lower two corners of the bar-magnet tracing.
4. one cm in from the lower two corners of the bar-magnet tracing.
5. two cm in from the lower two corners of the bar-magnet tracing.
6. four cm in from the lower two corners of the bar-magnet tracing.
SEE FIGURE 1 BELOW:
N
1
2
3
4
S
5
6
6
5
1
4
3
2
Figure 1 Setup for constructing magnetic field lines of a bar magnet
7. Place a compass at position 1 of the magnet.
8. Make two dots on the paper, one at the end of the compass needle next to the
magnet and the second at the other end of the compass needle.
9. Now move the compass so that the end of the needle that was next to the
magnet is directly over the second dot, and make a new dot at the other end of
the needle.
10. Continue this process until the compass comes back to the magnet or leaves the
edge of the paper. 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:
11. 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. 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 two magnets 15 cm apart, centered in the middle of the page. See figure three
below:
5. Position the compass in the locations indicated below, drawing dots at each end of the
compass as you go.
6. Connect the dots of the field lines indicated by the compass.
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.
N
S
Part 3: How Can We “See” the Earth’s Magnetic Field?
1. Place a bar magnet beneath a sheet of paper
2. Sprinkle iron filings above and around the bar magnet. Tap the edge of the
sheet of paper gently until a pattern is observed.
3. Trace the outline of the field lines as they are represented on the paper.
Part 4: Analysis
1. Describe how the field lines in Part 3 compare with your compass
markings in Part 1.
2. Look at the filings found along the poles. How are they aligned?
Describe.
3. Draw your best representation of what a 3 dimensional magnetic field will
look like.
4. How does each of these on-line resources help you to understand the
Earth’s magnetic field? Explain.
a. Go to the following sites and explore:
i. On-Line Magnetic Poles Demonstration
http://www.walter-fendt.de/ph14e/mfbar.htm
ii. Earth as a Magnet Interactive
http://www.windows2universe.org/physical_science/magn
etism/earth_magnet_dipole_interactive.html