Thermoelectric Effect Very Important Questions and answer
Thermoelectric Effect Very Important Questions Answer Collection
NEB Intermediate Science Faculty Grade XII Physics: Thermoelectric Effect very important Question answer collection is listed below and it contains Thermoelectric effect short question collection with the solution (answer).If you like this then feel free to share with your friends on different social media.
Short Questions with Answer (Solution)
1. What is thermo-electric e.m.f. ?
Ans. If we keep the junctions of two dissimilar metal making a loop at different temperatures, a current flows through it. An e.m.f. appears across the junction and is responsible for this current. This e.m.f. is called thermo-electric e.m.f. The value of thermo e.m.f. depends on :
The temperature of the hot junction of thermocouple and
The nature of the material chosen from the thermo-electric series
2. What do you mean by the Seebeck effect? (Seebeck effect notes)
Ans. The phenomenon of production of e.m.f. and hence current in a thermocouple when its two junctions are at different temperatures is known as Seebeck effect. Also, it is a reversible effect. According to the Seebeck effect equation the magnitude and direction of thermo e.m.f. and hence current depends upon :
The nature of the materials forming the thermocouple
Temperature difference between the two junctions.
3. How does the thermo-electric e.m.f. vary with the temperature?
Ans. The variation of thermo-electric e.m.f. ‘E’ with the temperature of hot unction ‘o’ is found as E = ao + bo Square, Where a and b are constants. This is a parabola shaped curved. At a certain temperature, it becomes maximum and that temperature is called neutral temperature, it becomes maximum and that temperature (Tn). On further increasing, it decreases and becomes again zero. After this temperature, e.m.f. is negative, which is called the temperature of inversion (T1 ).
4. Why is Sb-Bi thermocouple preferred to Fe-Cu thermocouple?
Ans. The device, which is made by two different temperature metal wires with their junction at different temperatures, is known as a thermocouple. The value of thermo e.m.f. produced between two elements two junctions of thermocouple depend on the position of the metal in the thermo-electric series. The more distant the two elements in this series, the larger is the thermo-electric e.m.f. for given differences of temperatures between the junctions of Fe and Cu is in the middle but the position of Sb and Bi is at the end. As a result, a large amount of thermo-electric current is produced by the Sb-Bi thermocouple than that by Fe-Cu thermocouple. That’s why Sb-Bi thermocouple preferred to Fe-Cu thermocouple.
5. What do you mean by Peltier’s effect?
Ans. When a current is passed through a thermocouple whose junctions are at the same temperature, heat is evolved at one junction who is thus heated and heat is absorbed in the other junction which is cooled. This is known as Peltier’s effect. This is the inverse see beck effect. If the direction of the current is reversed, the previous cold junction becomes hot.
6. What is the Thomson effect?
Ans. The absorption or evolution of heat when current is passed through an unequal heated conductor is called the Thomson effect. Heat absorbed or evolved in a small section of a wire is proportional to both the charge passed through it and the difference in temperature of the sections. There two types of Thomson effect:
Positive Thomson effect: If heat is evolved on flowing current from the end of higher to lower, it is called positive Thomson effect. The positive Thomson effect is found on metals like zinc, silver, antimony, etc.
Negative Thomson effect: If heat is absorbed on flowing current from the end of higher to lower, it is called negative Thomson effect. The negative Thomson effect is found on metals like cobalt, nickel, platinum, etc.
7. Why is a lead metal used as a reference metal in thermoelectricity?
Ans. The lead metal used as a reference metal in thermoelectricity because the Thermo e.m.f. of lead is almost zero. so, it is also used as a reference metal for thermoelectric constant a & B.
8. What is the effect of thermo-electric currents for precise measurement of current flowing in the circuits?
Ans. The thermoelectric current may often appear from small differences in purity of two samples of the same metal, and from the small difference of temperature due to warmth of the hand. In such a way, thermoelectric current can introduce error in measuring other small currents, not of thermal origin.
9. Seebeck effect is the resultant of Peltier’s and Thomson’s effects. Explain.
Ans. When the difference of temperature is maintained between the two ends of a thermocouple, the Peltier’s e.m.f. is developed at the two junctions. Experimentally it is found that the Seebeck e.m.f. is the algebraic sum of Peltier’s e.m.f. and Thomson e.m.f. That’s how; Seebeck effect is the resultant of Peltier’s effect and Thomson effect.
10. What are the two factors on which thermo-electric e.m.f. produce in a thermocouple depends?
Ans. The two factors on which thermoelectric e.m.f. produce in a thermocouple depends on (i) nature of two metals forming the thermocouple and (ii) temperature difference between two junctions of the thermocouple.
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