Thermocouple
Problem
How can electrical energy be obtained from thermal energy?
Hypothesis
We predict that the thermocouple will produce a very small amount of electricity when we heat it up to 100 degrees Celsius which should show on the galvanometer. We also predict that when we cool of the thermocouple at 2 degrees Celsius it will produce a greater amount of electricity Electricity and Heat
The conversion of electrical energy into thermal energy takes place in many household devices-for example, toasters, electric kettles, and electric coffee makers. On the other hand, a device such as the electric thermometer in a oven makes use of the conversion of thermal energy into electrical energy.
How can you get heat from electricity? You already know that when electrons travel through a wire, they collide whit the atoms of the wire. The greater the resistence in the wire, the greater the number of collisions, and the greater the amount of heat.
Thermoelectricity
Thermoelectricity, in physics, electricity generated by the application of heat to the junction of two dissimilar materials. If two wires of different materials are joined at their ends and one end is maintained at a higher temperature than the other, a voltage difference will arise, and an electric current will exist between the hot and the cold junctions. This phenomenon was first observed in 1821 by the German physicist Thomas Seebeck and is known as the Seebeck effect.
For a given combination of materials, the voltage difference varies in direct proportion to the temperature difference. This phenomenon can be utilized for the accurate measurement of temperature by means of a thermocouple in which one wire junction is maintained at a known reference temperature (for example, in an ice bath) and the other at the location where the temperature is to be measured. At moderate temperatures (up to about 2600 C/5000 F), wire combinations of iron and copper, iron and constantan (a copper-nickel alloy), and copper and constantan are frequently used. At high temperatures (up to 16490 C/30000 F), wires made from platinum and a platinum-rhodium alloy are employed. Because thermocouple wires can be made very small, they also provide a means for the accurate measurement of local spot temperatures. The current can be increased by using semiconductors instead of metals, and a few watts of power can be produced at efficiencies of up to 6 percent Transistor. Such thermoelectric converters, powered by kerosene lamps, are widely used in Russia and other republics of the Commonwealth of Independent States to provide power for radio receivers in remote areas.
The inverse effect occurs if current is sent through a circuit made of dissimilar materials, the junctions of which are at the same temperature. In this case, heat will be absorbed at one junction and given up at the other. This phenomenon is known as the Peltier effect for the French physicist Jean Peltier, who discovered it in 1834. Semiconductor systems operating on the Peltier effect can be used as low-powered miniaturized refrigerators for special applications.
ADVANTAGES OF THERMOELETCTRIC MODULES USAGE:
Cooling devises based on thermoelectric modules carry out the same cooling functions as traditional compression or absorption refrigerators working on special liquids.
However, the usage of thermoelectric modules being some kind of solid-state thermal pumps, has number of advantages:
> The absence of moving parts and working liquid in the cooling block;
> Small size and low weight of cooling system. An opportunity of micro coolers creation;
> High reliability of thermoelectric modules;
> Easiness of control and high tolerance temperature adjustment opportunity;
> Low cost at high overall performance.
Those specified advantages make thermoelectric modules very popular, which is also proved by ever increasing demand for this production all over the world and the occurrence of new application areas. However, if the above mentioned factors are not dominant, therefore, thermoelectricity can not be considered as a unique way of all cooling problems solving and, moreover, when making a decision for any particular task it is necessary to be guided by the comparison of "cost efficiency" criteria.
Materials:
20 cm bare thick copper wire
15 cm iron coated-hanger wire
2 connecting wires
galvanometer
heat source
pliers
beaker of ice-cold water
Procedure:
1) Coil about 5 cm of the copper wire tightly around the coated-hanger wire.
2) Attach the wire leads of the galvanometer to the copper-iron wire couple.
3) Observe and record the galvanometer.
4) Hold the coupled wires with a pair of pliers and, using the heat source, heat the junction of the wires; repeat Step 3.
5) Cool the junction in a beaker of ice-cold water; repeat Step 3.
Observations:
We observed at as the temperature started to rise, the electrical current started to rise as well. When we heated the wire up, the voltage on the voltage meter went up. This is caused when warm electrons collide with atoms of the wire and cause an electrical current. Then we put the hot wire in water and the electrical current started to rise even more. The current was even greater when we cooled the wire off because all the electrons rushed out at the same time, causing a greater current.
Conclusion:
Our hypotheses was only partly right because when we heated the thermocouple up we got a very small current, but when we cooled it off we got a much greater current of electricity then we thought that we would get.