(a) Resistance is defined as the property of a conductor due to which it opposes the flow of current through it. The S.I. unit of resistance is Ohm (Ω).

(b) (i) The resistance (R) of a conductor is related to its length (l) and area of cross section (A) as where ρis the resistivity of the conducting material Let R1 = Resistance of the original wire R2 = Resistance of the wire when its length is doubled l1 = Length of original wire l2 = Length of original wire when doubled A1 = Area of the original wire A2 = Area when it is halved Therefore, It is given that: l2 = 2l1 and Putting these values in equation we obtain R2 = 4 R1 Hence, the resistance of the wire will be 4 times of the original value.

(ii) The resistivity will not change on stretching the wire. Resistivity is the property of the conducting material. It does not depend on the dimension of the wire. As materials of both the wires are the same, the resistivity will not change.