chetan0412:
I am using voltage regulater IC 7805 to give supply to arduino but it gives higher current supply.I want to know the internal resistance of atmega 328 so that I use resistance in between the digital pin and 7805 to lessen the current
Ohms law doesn't apply to active devices, in general. It applies to conductors, semiconductors (if uniform, no PN junctions), electrolytes.
Batteries are basically made of plates and electrolyte and the internal resistance there is largely due to the ohmic resistance
of the electrolyte I think (although this is by no means constant with time / temperature or age).