Two wires have their lengths, diameters and resistivities all in the ratio of 1 : 2. If the resistance of the thinner wire is 10 ohm, the resistance of the thicker wire is :
(a) 5 ohm (b) 10 ohm (c) 20 ohm (d) 40 ohm
(b) Resistance (R) of a length l, resistivity r and area of cross-section A is given by
