$(a)$ Resistivity of iron is $10 \times 10^{-8} \;\Omega m$ and of mercury is $94 \times 10^{-8}\; \Omega m$. Which among iron and mercury is a better conductor ? Give reason.
$(b)$ Resistivity of a material $A$ is in the range of $10^{10}-10^{\text {14 }} \;\Omega m$ while that of $B$ is in the range of $10^{-6}-10^{-8} \;\Omega$ m. Which of the two will behave as an insulator and why?
$(a)$ Iron, because lower the resistivity, better is the conductor.
$(b)$ Material $A$, because insulators have higher resistivity.
What is meant by resistance of a conductor ? Name and define its $SI$ unit. List the factors on which the resistance of a conductor depends. How is the resistance of a wire affected if
$(i)$ its length is doubled,
$(ii)$ its radius is doubled. ?
Why alloys are used to make standard resistors ?
Define current, give its mathematical expression. What is its $SI$ unit ?
Why are alloys commonly used in electrical heating devices ?
Potential and potential difference are vector quantities.