For a metallic wire, the ratio of voltage to corresponding current is

In air, a charged soap bubble of radius ' $R$ ' breaks into 27 small soap bubbles of equal radius ' $r$ '. Then the ratio of mechanical force acting per unit area of big soap bubble to that of a small soap bubble is

Two parallel conductors carrying unequal currents in the same direction ............

A layer of atmosphere that reflects medium frequency radio waves which is ineffective during night, is