2007 PROTOTYPE Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio 1

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LESSON 3 ACTIVITY 3C, PART 1

Fat: Who Says?Measuring Obesity byBioelectrical Impedance AnalysisHuman Electrochemical CellActivity 3C Part 1Objectives:The students will be able to:

� Explain how an electrochemical cell works. � Explain how a human can be part of an electrochemical cell. � Determine which materials make the best electrodes in an

electrical cell. � Make observations and inferences; collect, graph, and

analyze data.

Activity Description:Engage: The teacher will hold up what looks like a ping-pong ball (theenergy ball) and ask the class to decide if it can be made to light up justby holding it. The teacher will hold the ball by two fingers, making surenot to touch the two electrical contacts on the bottom. The teacher then touches the two electrodes on the bottom of the ball so it lights up. After students have seen the Energy Ball demonstration, place them into groups and give each group an Energy Ball. Students try to duplicate what the teacher has demonstrated and explain what happened and why.

Explore: Students will learn how to use a multimeter as an ammeter todetermine if their bodies have any electrical current associated with it.

Explain: Students will become part of an electrochemical cell. By holding two different metals, one in each hand, and connecting thesemetals to a multimeter, the students will become part of a simple seriescircuit which will generate electrical current that can be measured in the microamps (μA) scale of a multimeter.

Activity Background:An electrochemical cell is a form of battery, composed of an electrolyteand electrical conductors. An electrolyte is a substance that containsatoms or groups of atoms with a charge (ions) and conducts electricity.Electrical conductors are materials that allow charged particles, such as electrons, protons, or ions to flow through them. When solid metal conductors are used, the flow of charged particles will involve only electrons. In the human body, the flow of charged particles consists of ions.

Batteries contain two electrical conductors (usually different types ofmetal) and they are called the electrodes. When a metal wire is connect-ed across the two ends (terminals) of a battery, an electric field acrossthe conductor is created. The moment contact is made; free electrons ofthe conductor are forced to drift toward the positive terminal under theinfluence of this field. The free electrons are responsible for the currentflow since a solid metal conductor is being used. The end (terminal) intowhich electrical current flows is the positive end. The end (terminal)from which the current flows is the negative end. A simple battery inyour flashlight is made this way; there is a carbon electrode inside thebattery and the metal case on the outside is the second electrode. See Figure 1.

The electrodes react chemically with the electrolyte (such as battery acidinside a battery), and this chemical reaction causes an electrical charge.The pair of electrodes must be made of different materials, such as cop-per and zinc. Different combinations of metals will produce batteries ofdifferent strengths (electrical potentials). In a battery with solid metalconductors, electrons flow from metal A to metal B. A multimeter willenable students to detect how much electron flow (current) is occurringin the battery. Current is measured in amperes (amps). See Figure 2.

2007 PROTOTYPE Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio 2

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LESSON 3 ACTIVITY 3C, PART 1

Positive terminal

Carbon red

Zinc can

Negative terminal

Figure 1 Simple Flashlight Battery

Figure 2 Simple Electrochemical Cell

NaCI

Metal B

Metal A - +

2007 PROTOTYPE Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio 3

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LESSON 3 ACTIVITY 3C, PART 1

Activity Materials:• 2 labeled pieces each of various metal, uniform in size*

(Note: 10” X 10” pieces would be the best but other sizes will work. You will need at least two pieces of each selected metal. Start with pieces of pure metals such as a copper, aluminum, zinc, lead and then add some galvanized steel.)

• 1 or more Energy Ball (s) (Analytical Scientific Part No. SAF-EB300 approximately $6)

• 2 electrical leads (24 gauge insulated telephone wire or leads with attached alligator clips from Radio Shack)

• 1 Analog Multimeter (Radio Shack 18-Range analog Multimeter - Part #22-223 suggested)

• 1 bottle of electrode gel - (It is recommended you make this gel. To make it you will need baby shampoo, water and table salt. The gel is made up of 40% volume of baby shampoo, 60% volume of water and 5% weight of salt. Making a large quantity of this material will enable all groups to use it in this and other parts of the activity.)

• Baby wipes to remove gel from hands

Activity Management Suggestions:� This activity can be set up as a station or a number of different

stations through which students rotate.� If materials are not readily available, you can set up a

demonstration for your students.� Laminate the Student Information Cards for re-use.� For many groups to participate at the same time, enough pieces

of pure metals should be provided so that each group can swap materials to test various combinations of metals.

� If enough metal objects are obtained, students should be given anopportunity to use all possible combinations of metals.

� An analog multimeter is used because it provides students an opportunity to incorporate math with science. Digital multimetersare difficult to read since the values often change as one is looking at the LED panel. This can be very confusing to a student. Students will be introduced to the multimeter and use it as an ammeter. The Radio Shack 18-Range analog Multimeter (Part #22-223) was used in the development and testing of this activity.

� If you are using a different multimeter, you may be able to go online and find instructions to give your students in place of those included in this activity.

� A simple handmade galvanometer can be made using bell wire and a compass. The handmade galvanometer will detect the presence of a current but will not give a quantifiable measure-ment on a change in the direction of flow.

2007 PROTOTYPE Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio 4

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LESSON 3 ACTIVITY 3C, PART 1

Modifications:1. Pair students in need of extra assistance with other students and

monitor closely to ensure that all participate fully in the activity.2. Students in need of extra assistance can be given specific tasks to

do as appropriate.

Extensions:1. Students can investigate how the surface area of the metal plates

changes the amount of current produced. Students can determine the area of the metal mathematically and measure the current. From their data, they can generate a ratio of current to square centimeter of area.

2. Students can bring different metallic objects from home to see if these objects can generate an electric current.

3. Students can investigate how alloys affect the amount of current produced.

4. Students can go on the Internet and research electrolytes in the human body.

5. Students can research the role of electricity in the human body. A suggested site might be Science News for Kids.www.sciencenewsforkids.orgGo to the Human Body collection of articles and look up the Oct 1, 2003 article called “Spark of Life.” Page 3.

6. Research other areas as well to look at how scientists are trying to harvest the energy of glucose molecules.

Activity References Used:Dawson, Trevor, Caputa, Krys, Stuchly, Maria,& Kravet, R. (2001).Electrical fields in the human resulting from 60-Hz contact currents.IEEE transactions on biometical engineering. 48, No. 9, 1020-1026.Sachse, FB, Werner, CD, Meyer-Waarden, K, & Dossel, O. (2000).Development of human body model for numerical calculation of electrical fields. Computer med imaging graphics, 24(3), 165-71.Websites:Cape Canaveral website:http://waww.geocities.com/CpeCanaveral/Hall/1410/lab-GS-24.html

Exploratorium Website:http://www.exploratorium.edu/snacks/hand_battery.html

Science Museum:http://www.sciencemuseum.org.uk/on-line/launchpad/441.asp

Science News for Kids website: http://www.sciencenewsforkids.org/articles/20031001/Feature1.asp

Spartech Software website:http://www.spartechsoftware.com/reeko/Experiments/ExpHumanBattery.htm

Sydney Morning Herald:http://www.smh.com.au/articles/2003/08/03/1059849278131.htm