RESISTANCE CONCEPT

Resistance :

                              The opposition offered by atoms against flow of electron called resistance .You can easily understand from fig.

UNIT:

                                        OHM or Ω 

Formula :

                                             R = V/I   =  VOLT/CURRENT

DEPENDENCE : 

                         RESISTANCE  α   temperature ,R α T

It mean increase of temperature resistance will also increase due to direct relation.

CASE :1(INCREASE)

                 Resistance increase with increase of temperature because increase of temperature the size of atom increases and than probability of collision of electron with atom increase due to this effect resistance increase with increase of temperature .Electron can not pass through metal or wire like this...

this bob can not pass through it due to expansion similarly this case also with electron in metal plate or wire . 

CASE :2(DECREASE)

                                                         Resistance decrease with increase of area of metal or wire with the increase of area the probability of collision of electron with the atom decreases because in large area electron are far away from atoms so they can easily move and can  conduct electricity or heat easily.