State Ohm's law. Calculate the conductivity of a conductor of radius 0.5 mm and length 10 cm having resistance `25 Omega`.

Calculate the capacity of the earth as a conduction sphere of radius 6.5 x 10^3 km.

Calculate the magnifying power of a magnifier of focal length 2.5 cm.

The resistance of N//5 solution of an electrolyte in a cell was found to be 45 ohm. Calculate the equivalent conductance of the solution if the electrodes in a cell are 2.2 cm apart and have an area of 3.8 equiv. cm.

Resistance of a conductivity cell filled with 0.1 M KCl solution is 100 ohms. If the resistance of the same cell when filled with 0.02 M KCl solution is 520 ohms, calculate the conductivity and molar conductivity of 0.02 M KCl solution. (The conductivity of 0.1 M KCl solution is 1.29 Sm^(-1) ).