. Bulletin of the scientific laboratories of Denison University. Thermo-electric Couples 247 gent 0. If 2c is negative, the line will slope downward from left to right. If the junctions are at U and h, the shaded area, fig. 2, repre- sents the electromotive force around the circuit, hence for metals M' and M" fig. 3, the shaded area represents the electromotive force when the junctions are at U and U. The ordinate, Tq of the point where the lines cross represents the neutral tempera- ture for those metals. It is customary to represent the thermo- electric power lines of all metals on one
. Bulletin of the scientific laboratories of Denison University. Thermo-electric Couples 247 gent 0. If 2c is negative, the line will slope downward from left to right. If the junctions are at U and h, the shaded area, fig. 2, repre- sents the electromotive force around the circuit, hence for metals M' and M" fig. 3, the shaded area represents the electromotive force when the junctions are at U and U. The ordinate, Tq of the point where the lines cross represents the neutral tempera- ture for those metals. It is customary to represent the thermo- electric power lines of all metals on one sheet, from such a sheet the direction and values of electromotive forces for given tem- peratures and given metals, as well as neutral points, may be determined. Peltier effect. Peltier, in 1834, observed that this thermo- electric effect is reversible, that when a current is sent around a circuit whose junctions are at the same temperatures, heat is. Heat generated Eeat absorbed cold hot cold oold hot cold Fig. 4. Thomson Effect. Positive effect. Direction of Current.— > Direction of heat travel.—> Fig. 5. Thomson Effect. Negative effect. Direction of Current.— > Direction of heat travel.*— absorbed at one junction, and generated at the other. This may be explained by assuming that there is a sudden change of poten- tial at the junctions, which is independent of the battery, and that the current does work in traversing this fall of potential. Thomson effect (figs. 4 and 5). Lord Kelvin, while trying to apply the reversible cycle of Carnot to the Peltier effect, con- cluded that were the Peltier effect the only reversible effect in the circuit, the electromotive force of the couple would be directly proportional to the difference in temperature of the junctions, which is contrary to observed facts. This led him, in 1851, to predict the existence of other effects, which he found, and which were' named after him, the Thomson Please note that these image
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