Press the switch and hold for two seconds. If the compass needle
reverses direction (Figure 2F), label this end of the coil S, and the
opposite end N. If the compass needle does not reverse, rotate the coil
180° and repeat the previous step.
Part 5: Orientation Trials
Use the compass to align the circular orientation arena (see Online
Materials) so the 0° label is facing magnetic north. Secure to the
table with tape. Magnetic north may vary depending on the amount
and location of iron used to construct the building, and this variation can be used as a discussion point for the class. Gently place the
pill bug in the center of the arena (circle) and cover it with the cap
from the tube. Allow the pill bug to rest for one minute. Remove
the cap, start the stopwatch, and monitor the pill bug as it walks
in the arena (Figure 3A). Mark the point where the pill bug first
crosses the circle’s boundary and record the angle to the nearest
10° tick mark (Figure 3B). If the pill bug does not cross the edge
within 60 seconds, repeat the trial. Repeat the orientation procedure 10 times (or more if time permits) with the same pill bug,
recording the angle for each trial. This is the “control” set.
Set up the pulse magnetizer so the N pole of the coil is facing up
(Figure 3C). Place the pill bug inside the plastic tube and insert the
tube inside the coil so the pill bug is approximately in the center
(Figure 3C). Press the switch to activate the pulse magnetizer and
hold for two seconds. Perform an orientation trial as described
above. Repeat for a total of at least 10 trials. This is the “pulsed”
group. The lab handout provided has areas for students to record
their orientation angles and the various behaviors they see.
Part 6: Data Analysis
Each group should plot their results and calculate the mean direction
in both the control and pulsed trials. Furthermore, students can test
for a preferred direction (nonrandom orientation, P < 0.05) using
the Rayleigh test and for a difference between the control and pulsed
Figure 2. (A) Materials necessary for building and testing
the pulse magnetizer, (B–D) steps to wrap the coil for it, and
(E–F) how to verify its function. The arrows emphasize the
change in direction of magnetic north before (E) and after
(F) the pulse magnetizer is activated.
Figure 3. (A) Performing an orientation trial with the pill bug and (B) recording the direction. The dashed line indicates the pill bug’s
movement, and the arrow represents how to record the angle (an example of 315° is shown). (C) Diagram representing how to expose
the pill bug to the magnetic pulse. The blue lines and arrows portray the direction of the magnetic field (north should point upward).