A cylinder of a material is $10\, cm$ long and has a cross-section of $2\, cm ^{2}$. If its resistance along the length be $20\, ohm$ what will be its resistivity in number and units ?

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.

The electric current flowing through any conductor is directly proportional to the electric potential difference across the conductor. Which law is this?

How many electrons will there be in $1.6\, C$ charge?

Find out the following in the electric circuit given in Figure.

$(a)$ Effective resistance of two $8\,\Omega $ resistors in the combination

$(b) $ Current flowing through $4\,\Omega $ resistor

$(c)$ Potential difference across $4\,\Omega $ resistance

$(d)$ Power dissipated in $4\,\Omega $ resistor

$(e)$ Difference in ammeter readings, if any.

Mention one reason why tungsten is used for making filament of electric lamp.