Apparatus Competition
2007 AAPT Summer Meeting
Greensboro, NC
Galvanize
Your Class
Robert
A. Morse
St. Albans School
Washington, DC 20016
202-537-6452
robert_morse@cathedral.org
Abstract
With inexpensive digital
multimeters and lengths of copper pipe, galvanized conduit and aluminum tubing
a group of students can quickly explore series and parallel combinations of
human Ôseats of emfÕ. This equipment extends the common science museum
demonstration of a hand battery into a cooperative group activity.
Construction of Apparatus:
Series battery: cut a number of 15 cm pieces from a length of ½ inch copper plumbing pipe, a length of ½ inch galvanized steel conduit and a length of 3/8 or ½ inch aluminum tubing. Connect dissimilar pieces with clip leads.
Parallel battery: Support 10 foot lengths of ½ inch copper pipe and ½ inch galvanized steel conduit horizontally with insulating supports about 20 to 30 centimeters apart.
Use of Apparatus:
Luigi Galvani and Alessandro Volta
moved electricity from the static electrification of Franklin and his followers
to the steady currents and voltages produced by electrochemical cells. A common
science museum demonstration[1]
consists of hand shaped metal plates of different metals. A visitor places a
hand on each plate and a meter shows a voltage. An inexpensive but sensitive
meter, some pieces of copper plumbing pipe, galvanized steel electrical conduit
and aluminum tubing, a few clip leads and a number of students allow you to
explore Òhuman batteriesÓ with different metals and with both series and
parallel combinations.
Students in series
Obtain 10 foot lengths of 1/2 inch
copper pipe, 1/2 inch galvanized steel conduit and 1/2 inch aluminum tubing and
cut into 15 cm pieces. Connect one lead of an inexpensive digital voltmeter set
to read DC volts to a copper piece and the other lead to a galvanized piece. If
a student grabs one piece of pipe in each hand the voltmeter will read about
0.7 volts. Connect a second pair of pipe pieces together with a clip lead. Put
two students in series. Voltmeter - copper pipe - student - galvanized pipe -
clip lead- copper pipe-student - galvanized pipe-voltmeter. The voltage reading
will increase. Continue adding students and pairs of clip connected pipes in
series up to the limit of students or pipe pairs. Try reversing some of the
pipe pairs and look at effect on voltage reading. Repeat with copper and
aluminum pipe pairs or galvanized and aluminum pipe pairs. Students can record
data and plot appropriate graphs. In my lab, a plot of voltage vs. number of
students was very nearly linear.
Students in parallel
Take a 10 foot length of 1/2 inch
copper pipe, and one of1/2 inch galvanized steel conduit.
Mount them horizontally on
insulated stands. Connect a
digital multimeter to the pipes set to read current on a sensitve scale.
Connect a second meter as a voltmeter to the two pipes.
Have a student grab one pipe with
each hand. Note current and voltage readings. Have a second student join the
line up- then a third, so that the students are in parallel along the pipes,
one hand grasping each pipe. Graph the current as a function of number of
students. Graph the voltage as a function of the number of students. In my lab
we got a nearly linear graph for current and a nearly constant value for
voltage, independent of the number of students.
Parallel set up
Educational value
The student involvement as part of
the apparatus of this experiment makes the experiment more interesting, and
emphasizes the difference between series and parallel connections by the
physical arrangement of the participating students. After the initial series
investigation with one pair of metals, producing the third kind of metal pipes
and having students design the rest of the investigation of the series combinations
allows student participation in designing the extension of the experiment.
Sample results
The following graphs show results
for series and parallel combinations of students in my classroom. The first
graph shows voltage versus number of students for series combinations of copper
and zinc, copper and aluminum and aluminum and zinc electrodes. The second
graph shows current versus the number of students for copper and zinc
electrodes in parallel.
Galvanize your class series data.
Galvanize your class parallel data
Equipment and costs required to construct apparatus:
|
Item |
Source |
Part number |
Cost |
|
3 Cen-Tech Digital
Multimeters |
Harbor Freight Tools |
90899-1RVB |
$3 each |
|
2 10 ft ½ inch
copper pipe |
Hardware store |
|
$12.70 each |
|
2 10
ft ½ inch galvanized conduit |
Hardware store |
|
$3.20 each |
|
1 6
ft 3/8 inch aluminum tube |
Hardware store |
|
$8.80 |
|
10
short clip leads |
Lab equipment |
|
|
|
2 x
6 lumber, screws, 4 pipe clips |
Scrap box |
|
|
1 Total Cost |
$49.60 |
||