What is resistance? How is resistance caused. What are the factors it depends? How does it vary with temperature?

The resistance of a conductor is the ratio of potential difference between the ends of a conductor to the current flowing through it. Resistance = ⇒ R = S. I. unit of resistance is ohm. 1 ohm = . As electrons inside a conductor are not entirely free to move, their motion is restrained by the attraction to the atoms. This retards the motion of electrons through the conductor, and is called resistance. The resistance of a conductor depends on its length, cross sectional area and resistivity. R = ρ (Where l is length, A is cross sectional area, ρ is resistivity). As resistivity changes with temperature, resistance also depends on temperature. Resistance of a conductor increases with increase in temperature.