Resistance is the property of a conductor that opposes the flow of charge through it. It is given by $R=\frac{V}{I}$ where $V=$ potential difference across the conductor and $I=$ current through the conductor.

The resistance of conductor depends on the length, area of cross-section and nature of material of the conductor.

It also depends on the temperature of the conductor.

If $\rho$ be the resistivity of the material of the conductor, $l$ be its length and $A$ be its area of cross-section, answer the following question:

When a potential difference of $12.5 \mathrm{V}$ is applied across the conductor, $0.5 \mathrm{A}$ of current flows through it. Its resistance is

Metals have very low resistivities because of which they are good conductors of electricity. Resistivities of alloys like nichrome and manganin are $25 – 100$ times more than those of metals while resistivities of insulators are very high.

The resistivities of five materials are given as under:

$\mathrm{P}: 1.70\times {10}^{-8} \mathrm{\Omega m}$

$\mathrm{Q}: 2.60\times {10}^{-8} \mathrm{\Omega m}$

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

$\mathrm{S}: 1.0\times {10}^{13} \mathrm{\Omega m}$

$\mathrm{T}: 110\times {10}^{-8} \mathrm{\Omega m}$

Now answer the following question:

Which of the above material is the best conductor of electricity?

Metals have very low resistivities because of which they are good conductors of electricity. Resistivities of alloys like nichrome and manganin are $25 - 100$ times more than those of metals while resistivities of insulators are very high.

The resistivities of five materials are given as under:

$\mathrm{P}: 1.70\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

$\mathrm{Q}: 2.60\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

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

$\mathrm{S}: 1.0\times {10}^{13} \mathrm{\Omega } \mathrm{m}$

$\mathrm{T}: 110\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

Now answer the following question:

How is the resistivity of material $\text{'}\mathrm{S}\text{'}$ expected to change with increase in temperature?

Metals have very low resistivities because of which they are good conductors of electricity. Resistivities of alloys like nichrome and manganin are $25 - 100$ times more than those of metals while resistivities of insulators are very high.

The resistivities of five materials are given as under:

$\mathrm{P}: 1.70\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

$\mathrm{Q}: 2.60\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

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

$\mathrm{S}: 1.0\times {10}^{13} \mathrm{\Omega } \mathrm{m}$

$\mathrm{T}: 110\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$

Now answer the following question:

Which of the materials would you advise to be used for making heating elements of electric irons?

Resistivities of some materials are given below

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

$\mathrm{Q}: 1.0\times {10}^{10}\mathrm{\Omega m}$

$\mathrm{R}: 2.3\times {10}^3\mathrm{\Omega m}$

$\mathrm{S}: 110.0\times {10}^{-8}\mathrm{\Omega m}$

Now match the materials in Column I to the items in Column II.

Match the resistivities of materials given in Column I to the practical uses of each material in Column II.