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Instructor Outline: UM Physics Demo Lab 07/2013 Electrochemical Cells and Batteries Lab length: 70 minutes Lab objective: Instruct the students about electrochemical cells, batteries, electrolytes, anodes, cathodes, voltage, current, resistance and the use of a multimeter. Materials 2 plastic beakers 2 metal bars (1 Cu, 1 Zn) 1 U-bar, Cu & Zn Stack of Cu & Zn disks paper disks Cup of Coke (battery acid) 2 plastic spacers 1 Green multimeter 2 banana leads with alligator clips 1 special calculator 1 blue plastic tray (coke containment) Aluminum foil Paper towels Sandpaper Suggested Demonstrations: Dissected Batteries 5E20.10 - Electrolysis of Water 5E40.25 - Lemon Battery 5A50.30 – Van de Graaff Generator & components Exploration stage: 30 minutes – Group Lab-Work The students build coke batteries. They observe the role of electrolytes in a battery, and how series results in a voltage increase. The students then power a calculator with their coke battery. Analysis stage: 10 minutes – Lecture The instructor analyzes the findings in the exploration stage, and answers questions formed during that stage. Concept development is done on cells, electrolytes, anodes and cathodes, batteries as connected networks of cells, voltage, current, conventional current and resistance. The students can use the analysis text to follow during the lecture, read it at a later time, or use it as a reference only. Application stage: 20 minutes – Group Lab-Work The students build batteries with strips of electrolyte soaked paper. They are challenged to build a 6V battery, but 4.5V is the actual maximum we’ve observed. Summary: 10 minutes – Lecture This is a final opportunity for questions to be addressed. This is time to re-iterate the core concepts and principles. Concepts developed: 1. Electrochemical cells are very simple devices constructed from an electrolyte solution, a cathode metal (positive terminal), and an anode metal (negative terminal). 2. Cells work by electrochemically separating charge and making it energetically favorable for electrons to flow from higher electrical potential energy to lower electrical potential energy, that is, from the negative anode to the positive cathode. Property of LS&A Physics Department Demonstration Lab Copyright 2006, The Regents of the University of Michigan, Ann Arbor, Michigan 48109 3. Traveling electrons are a current; the path they take is the resistance of the external circuit. The electric potential energy available per electron is the difference in electrical potential or voltage between the anode and cathode. 4. Electrons flow from the negative anode to the positive cathode when a cell or battery is connected to an external circuit. 5. Conventional current is defined as the flow of positive charges from the positive cathode terminal of a cell or battery to the negative anode terminal. This is a commonly used engineering convention and is completely equivalent to the actual flow of negative electrons from the negative anode to the positive cathode which actually takes place in any real circuit. 6. Cells may be connected together to form batteries. 7. Cells connected in series provide a difference in electrical potential which is the sum of the potential differences for the individual cells. Cells connected in series provide the same current as a single cell. 8. Cells connected in parallel can provide more current at the same potential difference as a single cell. Property of LS&A Physics Department Demonstration Lab Copyright 2006, The Regents of the University of Michigan, Ann Arbor, Michigan 48109