Resistance and resistivity ( By pak physics)

Opposition offered by the material of conductor in the flow of electric current is called resistance.
Resistance opposes the flow of current through a conductor. Resistance of a conductor is due to the collision of free electrons with the atoms of the conductor.
It is denoted by “R”

(1) Length of conductor
Resistance of a conductor is directly proportional to the length of conductor .
R a L…………….(a)
(2) Area of cross section of conductor
Resistance of a conductor is inversely proportional to area of cross section of conductor.
R a 1 / A……………….(b) Combining (a) and (b)                                                                       R α L/A                                                 R = rL/A Where  r = resistivity of material of conductor RESISTIVITY Resistivity is an electrical property of material . It is defined as the resistance of a material or conductor of 1 cubic meter volume.                                         Or It is the resistance of a conductor of unit length and unit area.                                         Or Resistivity of a conductor is the resistance of 1 meter long conductor whose area of cross section is  I meter square Unit: R = rL/A     r = ohm x m Different materials have different values of resistivity. A very high value of resistivity indicates high electrical resistance