Question

A copper strip AB and an iron strip AC are joined at A. The junction A is maintained at $0^\circ {\text{C}}$ and the free ends are maintained at $100^\circ {\text{C}}$. There is a potential difference between (This question has multiple correct answers).
A. the two ends of the copper strip
B. the copper ends and the iron end at the junction
C. the two ends of the iron strip
D. the free ends B and C

Answer 1

Recall the principle of thermoelectric effect or Seebeck effect. Draw the diagram showing the arrangement and temperature of the copper strips and iron strips. Using this diagram, check the temperature difference between the various ends of the given arrangement and check whether the potential difference is developed between these two ends or not.

Complete answer:
We have given that a copper strip AB and an iron strip AC are connected at point A and the junction is formed at the point A.The temperature of the junction point A is $0^\circ {\text{C}}$ and the temperature of the free ends of the copper and iron stripes B and C is $100^\circ {\text{C}}$. We are asked to determine that across which two ends of these two strips the potential difference is developed.According to the thermoelectric effect or Seebeck effect, a potential difference is developed between the two ends of the dissimilar conductors when there is temperature difference between these two ends of the conductor.Using this principle, let us check across which ends of the copper and iron strips potential difference is developed.

The diagram representing the arrangement of the copper and iron strips is as follows:

From the above diagram, we can see that there is a temperature difference of $100^\circ {\text{C}}$ between the two ends of the copper strip. Therefore, there must be a potential difference between the two ends A and B of the copper strip.Hence, the option A is correct.The electron density difference is there between the copper and iron. Therefore, the potential difference will be between the end of the copper and iron at the junction due to this electron density.Hence, the option B is correct.

From the above diagram, we can see that there is a temperature difference of $100^\circ {\text{C}}$ between the two ends of the iron strip. Therefore, there must be a potential difference between the two ends A and B of the iron strip.Hence, the option C is correct.There will be a temperature difference between the free ends B and C to attain equilibrium. Hence. The potential difference will be developed between the ends B and C of the strips.Hence, the option D is correct.

Hence, the correct options are A, B, C and D.

Note: The student should not get confused that the temperature of the copper strip and iron strip at the junction point A is the same. Then how the potential difference is developed at point A. But the electron density is different for the copper strip and iron strip which develops the potential difference at this point.