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 ‘seats of emf’. 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 “human batteries” 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

 



[1] Ron Hipschman, "Hand Battery," Exploratorium Cookbook II, p. 91.1 - 91.2.