The equivalent capacitance of the arrangement shown in figure is:

A certain wire $$\mathrm{A}$$ has resistance $$81 ~\Omega$$. The resistance of another wire $$\mathrm{B}$$ of same material and equal length but of diameter thrice the diameter of A will be :

A copper wire of radius $$1 \mathrm{~mm}$$ contains $$10^{22}$$ free electrons per cubic metre. The drift velocity for free electrons when $$10 \mathrm{~A}$$ current flows through the wire will be (Given, charge on electron $$=1.6 \times 10^{-19} \mathrm{C}$$ ) :

To produce an instantaneous displacement current of $$2 \mathrm{~mA}$$ in the space between the parallel plates of a capacitor of capacitance $$4 ~\mu \mathrm{F}$$, the rate of change of applied variable potential difference $$\left(\frac{\mathrm{dV}}{\mathrm{dt}}\right)$$ must be :-