# Thermoelectric Effect – Short Questions Collection With Answer | Physics Class 12

## Very Important Questions Collection HSEB | Science Faculty Thermoelectric Effect – Physics Grade XII Short Questions with Answer (Solution)

1. What is thermoelectric 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 thermoelectric e.m.f. The value of thermo e.m.f. depends on :

• The temperature of hot junction of hot junction of thermocouple and
• The nature of material chosen from the thermoelectric series

2. What do you mean by seebeck effect?
Ans. The phenomenon of production of e.m.f. and hence current in athermocouple when its two junctions are at different temperatures is known as seeback effect. Also, it is reversible effect.The magnitude and direction of thermo e.m.f. and hence current depends upon :

1. The nature of the materials forming the thermocouple
2. Temperature difference between the two junctions.

3. How does the thermoelectric e.m.f. vary with the temperature?
Ans. The variation of thermoelectric 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 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 temperature, is known as thermocouple.The value of thermo e.m.f. produced between two elements two junctions of thermocouple depends on the position of metal in the thermoelectric series. The more distant the two elements in the thermoelectric series, the larger is the thermoelectric e.m.f. for a given differences of temperatures between the junctions of Fe and Cu is at middle but the position of Sb and Bi is at end. As a result, large amount of thermoelectric current is produced by 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 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 at 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 Thomson’s effect ?
Ans. The absorption or evolution of heat when current is passed through an unequal heated conductor is called Thomson’s 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’s effect:

1. 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.
2. 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 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 thermoelectric currents for precise measurement of current flowing in the circuits?
Ans. The thermoelectric current may often appears from small differences in purity of two samples of the same metal, and from small difference of temperature due to warmth of the hand. In such 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 effect. Explain.
Ans. When 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 thermoelectric 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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