constructed by tightly wrapping the electrical wire around the PVC
pipe, leaving ~5 cm excess on either end available for connections
(Figure 2B–D). The rubber bands can be applied to either end of
the coil to secure the wire and prevent the coil from loosening. Con-
nect one lead of the coil to one terminal of the switch, then connect
the remaining terminal of the switch to the positive (red) lead of the
battery connector (the instructor may prepare this ahead of time as
described above). Connect the positive (red) probe of the ammeter/
multimeter to the other lead from the coil and the negative probe
(black) to the negative lead (black) from the battery connector. This
connection is temporary – just to read current – and the use of
alligator clips may help (Table 3). Set the multimeter to record cur-
rent (in amperes) and connect the battery to the circuit. Press the
switch, hold for two seconds, and record the maximum current in
amps. Repeat three times and note the reading each time in the
“Constructing the Pulse Magnetizer” portion of the lab handout. Dis-
connect the multimeter and connect the negative battery lead (black)
to the coil. Cover all connections with electrical tape.
To estimate the strength of the magnetic field inside the coil,
use the equation (from Purcell, 1985, section 6.5)
where B is the field strength in Tesla (T), u0 is the permeability of
free space ð4π × 10−7 T ⋅ m ⋅ A−1Þ, N is the number of turns (wraps)
in the coil, L is the length of the coil in meters (length of PVC pipe
covered with wire coils), and I is the current measured in amperes
(A; average of the three measurements taken). Both N and L can
be measured by counting the number of turns of wire and measuring
the length of the coil (in meters) with a ruler, respectively. Students
can record the estimated strength of their magnetic field coil in the
“Constructing the Pulse Magnetizer” portion of the lab handout
Part 4: Verify the Pulse Magnetizer’s Function
The goal is to identify the north (N) and south (S) poles of the electromagnet created when electric current passes through the coil.
First, allow the compass needle to align with magnetic north and
place one end of the coil facing the north compass point (Figure 2E).
Table 3. List of materials required for this activity.
Required Items Example
9-volt battery Amazon (no. B00MH4QM1S)
9-volt battery connector,
Amazon (no. B06X8YZJ64)
2 m insulated wire (24
gauge), ends stripped
Mouser Electronics Inc. (no. 566-
(normally open, or NO)
Amazon (no. B01IU898QA)
4 cm length × 2 cm
diameter (3/4 in) PVC pipe
Amazon (no. B003OSKZF0)
Two to four 1.5 cm
Amazon (no. B007PJ4Z82)
Compass Carolina Biological Supply Co.
Ammeter/multimeter Carolina Biological Supply Co.
Electrical tape Carolina Biological Supply Co.
Pill bug (Armadillidium
Field collected or Carolina
Biological Supply Co. (no. 143080)
76 × 20 mm plastic tube Sarstedt AG & Co. (no. 80.734,
Stopwatch Carolina Biological Supply Co.
Ruler Carolina Biological Supply Co.
Paper orientation arena See Online Materials for a
Optional Items Example
DC magnetometer AlphaLab Inc. (no.
Alligator clips Carolina Biological Supply Co.
470 Ohm resistor Amazon (no. B0185FIDF0)
5 mm LED Amazon (no. B005ONQ41W)
Figure 1. Wiring diagrams demonstrating how to build the
pulse magnetizer circuit (A) with the ammeter/multimeter and
(B) without the ammeter/multimeter. (C) An example circuit
with the addition of a light-emitting diode (LED) and 470 Ω
resistor that illuminates when the pulse magnetizer is switched
on. The directions of current (solid arrow) and electron flow
(dashed arrow) are shown in A.