Resistance is the property of a substance due to which it opposes the flow of current through it. The unit of resistance is ohm (Ω).
A conductor shown in Figure A.1 is taken length = l m and area of cross-section = a m2.
If R is its resistance, we have
R ∝ l when a is constant.
R ∝ when l is constant.
R ∝ when both l and a are not constant.