What are the factors on which the resistance of a conductor depends?

State Ohm's law. How can it be verified experimentally? Does it hold good under all conditions? Comment.

State the factors on which the resistance of a cylindrical conductor depends. How will the resistance of a conductor change if it is stretched so that its length is doubled?

Use the data in the table to answer the following: Which material is the best conductor?

Material	Resistivity $(\Omega \,m)$
Silver	$1.6 \times 10^{-8}$
Copper	$1.62 \times 10^{-8}$
Aluminium	$2.63 \times 10^{-8}$
Tungsten	$5.20 \times 10^{-8}$
Nickel	$6.84 \times 10^{-8}$
Iron	$10.0 \times 10^{-8}$
Chromium	$12.9 \times 10^{-8}$

Define electric current and state its $SI$ unit. With the help of $Ohm's$ law,explain the meaning of $1$ ohm resistance.

$A$ potential difference $V$ is applied across a conductor of length $L$ and diameter $D$. How is the resistance $R$ of the conductor affected,when in turn $(i)$ $V$ is halved,$(ii)$ $L$ is halved,and $(iii)$ $D$ is doubled? Justify your answer in each case.