Use the data in the table to answer the following: Which among iron and mercury is a better conductor?
< p style="text-align:center"> < span style="font-size:14px"> Electrical resistivity of some substances at $20\,^oC$

Material	Resistivity $(\Omega \,m)$
Iron	$10.0 \times 10^{-8}$
Mercury	$94.0 \times 10^{-8}$

The values of current $I$ flowing in a given resistor for the corresponding values of potential difference $V$ across the resistor are given below -

$I$ (amperes)	$0.5$	$1.0$	$2.0$	$3.0$	$4.0$
$V$ (volts)	$1.6$	$3.4$	$6.7$	$10.2$	$13.2$

Plot a graph between $V$ and $I$ and calculate the resistance of that resistor.

Explain the term resistance. Give its $SI$ unit of measurement.

Define resistance of a conductor. State the factors on which resistance of a conductor depends. Name the device which is often used to change the resistance without changing the voltage source in an electric circuit.
Calculate the resistance of $50 \, m$ length of wire of cross-sectional area $0.01 \, mm^2$ and of resistivity $5 \times 10^{-8} \, \Omega \, m$.

Resistance of a metal wire of length $1\, m$ is $26\, \Omega$ at $20^{\circ} C$. If the diameter of the wire is $0.3\, mm$,what will be the resistivity of the metal at that temperature?

What can be the difference between the specific resistance for a thin and thick wire made of the same material?