$1.$ In the graphs below, the resistance $\mathrm{R}$ of a superconductor is shown as a function of its temperature $\mathrm{T}$ for two different magnetic fields $\mathrm{B}_1$ (solid line) and $\mathrm{B}_2$ (dashed line). If $\mathrm{B}_2$ is larger than $\mathrm{B}_1$ which of the following graphs shows the correct variation of $\mathrm{R}$ with $\mathrm{T}$ in these fields?
MCQ $Image$
$2.$ A superconductor has $T_C(0)=100 \mathrm{~K}$. When a magnetic field of 7.5 Tesla is applied, its $\mathrm{T}_{\mathrm{c}}$ decreases to $75 \mathrm{~K}$. For this material one can definitely say that when
$(A)$ $\mathrm{B}=5$ Tesla, $\mathrm{T}_{\mathrm{c}}(\mathrm{B})=80 \mathrm{~K}$
$(B)$ $\mathrm{B}=5$ Tesla, $75 \mathrm{~K}<\mathrm{T}_{\mathrm{c}}(\mathrm{B})<100 \mathrm{~K}$
$(C)$ $\mathrm{B}=10 \mathrm{Tesla}, 75 \mathrm{~K}<\mathrm{T}_{\mathrm{c}}<100 \mathrm{~K}$
$(D)$ $\mathrm{B}=10$ Tesla, $\mathrm{T}_{\mathrm{c}}=70 \mathrm{~K}$
Give the answer question $1, 2$
- ✓$(A,B)$
- B$(B,C)$
- C$(A,D)$
- D$(B,D)$
