A) \[100{}^\circ C\]
B) \[300{}^\circ C\]
C) \[400{}^\circ C\]
D) \[500{}^\circ C\]
Correct Answer: C
Solution :
Key Idea: Thermo emf becomes zero at temperature of inversion. As temperature of hot junction rises the thermo emf E increases and becomes maximum and then decreases with rise in temperature and ultimately becomes zero at temperature of inversion. Given, \[E=AT-\frac{1}{2}B{{T}^{2}}\] When \[E=0,T={{T}_{i}}\] \[\therefore \] \[A{{T}_{i}}-\frac{1}{2}BT_{i}^{2}=0\] \[\Rightarrow \] \[{{T}_{1}}=\frac{2A}{B}\] Putting, \[A=16,B=0.08,\]we get \[{{T}_{i}}=\frac{2\times 16}{0.08}=400{{\,}^{o}}C\] Note: If the temperature of hot junction is further increased beyond the temperature of inversion, the emf is produced in the opposite direction.
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