The voltage - current $(V-I)$ graph of a metallic conductor at two different temperatures, $T_1$ and $T_2$ is shown in the figure. At which temperature is the resistance higher?

 

Vagisha and Ryan perform experiments on two given resistors $R_1$ and $R_2$. They get the following plots:  

If it is given that $R_1>R_2$, whose graph represents the situation correctly? Justify your answer.

The electrical resistivities of a few materials are given below in ohm-metre. Which of these materials can be used for making element of a heating device?

Electrical resistivities of some substances at $20°\mathrm{C}$ are given below:

Silver : $1.60\times {10}^{-8} \mathrm{\Omega } {\mathrm{m}}^{}$

Copper : $1.62\times {10}^{-8} \mathrm{\Omega } {\mathrm{m}}^{}$

Tungsten : $5.20\times {10}^{-8} \mathrm{\Omega } {\mathrm{m}}^{}$

Iron : $10.0\times {10}^{-8} \mathrm{\Omega } {\mathrm{m}}^{}$

Mercury : $94.0\times {10}^{-8} \mathrm{\Omega } {\mathrm{m}}^{}$

Nichrome : $10.0\times {10}^{-6} \mathrm{\Omega } {\mathrm{m}}^{}$

Answer the following question in relation to them:

Among silver and copper, which one is a better conductor? Why?

Electrical resistivities of some substances at $20 °\mathrm{C}$ are given below:

Silver : $1.60\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

Copper : $1.62\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

Tungsten : $5.20\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

Iron : $10.0\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

Mercury : $94.0\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

Nichrome : $10.0\times {10}^{-6} \mathrm{\Omega } \mathrm{m}$

Answer the following question in relation to them:

Which material would you advise to be used in electrical heating devices? Why?