JEE Advanced · Physics · 19. Current Electricity
Paragraph :
Electrical resistance of certain materials, known as superconductors, changes abruptly from a non-zero value to zero as their temperature is lowered below a critical temperature \(T_C(0)\). An interesting property of superconductors is that their critical temperature becomes smaller than \(T_C(0)\) if they are placed in a magnetic field i.e., the critical temperature \(T_C(B)\) is a function of the magnetic field strength \(B\). The dependence of \(T_C(B)\) on \(B\) is shown in the figure.

Question :
A superconductor has \(T_C(0)=100 \mathrm{~K}\). When a magnetic field of \(7.5\) Tesla is applied, its \(T_C\) decreases to \(75 \mathrm{~K}\). For this material one can definitely say that when (Note : \(\mathrm{T}\) = Tesla)
- A \(B=5 \mathrm{~T}, T_C(B)=80 \mathrm{~K}\)
- B \(B=5 \mathrm{~T}, 75 \mathrm{~K} < T_C(B) < 100 \mathrm{~K}\)
- C \(B=10 \mathrm{~T}, 75 \mathrm{~K} < T_C(B) < 100 \mathrm{~K}\)
- D \(B=10 \mathrm{~T}, T_C(B)=70 \mathrm{~K}\)
Answer & Solution
Correct Answer
(B) \(B=5 \mathrm{~T}, 75 \mathrm{~K} < T_C(B) < 100 \mathrm{~K}\)
Step-by-step Solution
Detailed explanation
With increase in temperature, \(T_C\) is decreasing.
\(
\begin{aligned}
T_C(0) & =100 \mathrm{~K} \\
T_C & =75 \mathrm{~K} \text { at } B=7.5 \mathrm{~T}
\end{aligned}
\)
Hence, at \(B=5 \mathrm{~T}, T_C\) should lie between \(75 \mathrm{~K}\) and \(100 \mathrm{~K}\). Hence, the correct option should be (b).
\(
\begin{aligned}
T_C(0) & =100 \mathrm{~K} \\
T_C & =75 \mathrm{~K} \text { at } B=7.5 \mathrm{~T}
\end{aligned}
\)
Hence, at \(B=5 \mathrm{~T}, T_C\) should lie between \(75 \mathrm{~K}\) and \(100 \mathrm{~K}\). Hence, the correct option should be (b).
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