



In wire-bound standard resistors, it is crucial to have a stable resistivity with changes in temperature to ensure accurate and consistent resistance values. This implies that the ideal resistivity (\(\rho\)) vs. temperature (T) curve should show minimal variation in resistivity when temperature changes. The curve that best fits this requirement would be one that is relatively constant, i.e., a horizontal line, indicating resistivity remains the same despite temperature fluctuations.
Looking at the options, the curve in
represents a situation where resistivity does not change noticeably with temperature. Therefore, this is the most suitable choice for wire-bound standard resistors, as it suggests a resistivity that is largely independent of temperature changes, maintaining reliability and precision in resistance values.
Concept:
For wire-bound standard resistors, the material used should have a very small temperature coefficient of resistivity — meaning its resistivity should remain almost constant with change in temperature.
Explanation:
If resistivity \( \rho \) changes significantly with temperature \( T \), the resistance of the wire will also vary, making the resistor unsuitable as a standard (since it won’t give a constant resistance value).
Thus, the most suitable \( \rho \)-vs-\( T \) curve is the one where \( \rho \) remains nearly constant over a wide range of temperature (a nearly horizontal line).
Hence, the correct option is:
Option 1 — the graph showing almost constant resistivity with temperature.
A black body is at a temperature of 2880 K. The energy of radiation emitted by this body with wavelength between 499 nm and 500 nm is U1, between 999 nm and 1000 nm is U2 and between 1499 nm and 1500 nm is U3. The Wien's constant, b = 2.88×106 nm-K. Then,

Three voltmeters, all having different internal resistances are joined as shown in figure. When some potential difference is applied across A and B, their readings are $V_1$, $V_2$ and $V_3$. 
Choose the correct option.
What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)