According to ohm's law, physical conditions like temperature remaining constant and the current passing through a conductor experiences a force. where current is directly proportional to the voltage(potential difference) across the two ends.
In this V is voltage, I is current and R is resistance.Here R is constant.
It is used for calculating current through the conductor like D.C and AC current. Tells about the resistance in the circuit and voltage across the circuit.

V is directly proportional to I. where R is constant.
When temperature remains constant,current passing through a current carrying conductor is directly proportional to the potential difference developed between its ends. that is I is directly proportional to the p.d ie voltage  .V=IR  where R is the resistance