Objective
The goal of this project is to investigate thermoelectricity. How much voltage can be generated between two junctions made of different conductive materials held at different temperatures? Can you create a temperature difference between two junctions made of different conductive materials by passing a current through them?
Introduction
Thermal energy (heat) is one of the oldest forms of energy known to mankind. Thermal energy is usually a byproduct of other forms of energy such as chemical energy, mechanical energy, and electrical energy. The process in which electrical energy is transformed into thermal energy is called Joule heating. This is what causes wires to heat up when current runs through them, and is the basis for electric stoves, toasters, etc.
Transforming thermal energy into electrical energy is known as the Seebeck effect, discovered by J.T. Seebeck in 1821. Seebeck discovered that making one end of a metal bar hotter or colder than the other produced an electric voltage between the two ends. Seebeck experimented with junctions (simple mechanical connections) made between different conducting materials. He found that if he created a temperature difference between two electrically connected junctions (e.g., heating one of the junctions and cooling the other) the wire connecting the two junctions would cause a compass needle to deflect. He thought that he had discovered a way to transform thermal energy into a magnetic field. Later it was discovered that he had created a simple electric current loop, which produced a magnetic field. (See the Science Buddies project idea: Using a Magnet as an Electric Current Detector.)
The magnitude of the voltage produced between two junctions depends on the materials used to create the junctions and on the temperature difference between them. The diagram in Figure 1 shows how you can measure the voltage that is produced. The red and black lines represent wires made of different materials. For example, let's say the black line is an iron wire, and the red lines are copper wires. The wires are twisted together at the points where they touch, forming a junction. One of the junctions is heated (that's a candle, on it's side, heating the junction with it's flame), and the other is cooled (on a block of ice). The voltmeter measures the electrical potential (voltage) between the two junctions.
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| Figure 1. Diagram of experimental setup for measuring the Seebeck effect. |
The reverse of the Seebeck effect is also possible: by passing a current through two junctions, you can create a temperature difference. This process was discovered in 1834 by scientist named Peltier, and thus it is called the Peltier effect. This may sound similar to Joule heating described above, but in fact it is not. In Joule heating the current is only increasing the temperature in the material in which it flows. In Peltier effect devices, a temperature difference is created: one junction becomes cooler and one junction becomes hotter. Although Peltier coolers are not as efficient as some other types of cooling devices, they are accurate, easy to control, and easy to adjust. Peltier effect devices are used coolers for microelectronic devices such as microcontrollers and computer CPUs. This use is very common among computer hobbyists to help them in over-clocking the microprocessors for more speed without causing the CPU to overheat and break in the process.
In this starter kit we will describe how to create an experiment to demonstrate the Seebeck effect and Peltier effects and some variations on them.
Terms, Concepts and Questions to Start Background Research
To do this project, you should do research that enables you to understand the following terms and concepts:
Bibliography
Materials and Equipment
To do this experiment you will need the following materials and equipment:
Experimental Procedure
Before starting the experiment, do your background research so that you are knowledgeable about the terms and concepts above.
Measuring the Seebeck Effect
Measuring the Peltier Effect
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| Figure 2. Diagram of experimental setup for measuring the Peltier effect. |
Variations
Credits
By Akram Salman 
Edited by Andrew Olson, Ph.D., Science Buddies
Last edit date: 2006-06-05 13:45:00
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