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Let me first define some terminology:
1) voltage = difference in potential,
if you traverse the circuit element (resistor, source, capacitor,
inductor) in the one direction, the potential will rise and in the
other the potential will drop.
It is essential to assign current directions AND values to each
element, too. ----> 3A is exactly the same as (-3A) <-----, so the
direction arrow and value are inseparable.
Most circuits drawn in introductory physics don't have a reference ground shown
so you can't talk about either the potential or the voltage at a point.
With this current and voltage notation, Ohms Law becomes tied to a
sign convention of the voltage across and conventional current
through a resistor: Traditionally, V = IR is true if V is the number
attached to the voltage polarity across the resistor and I is the
number attached to the conventional current flowing in the direction
from the + to the - sign (or entering the + polarity assignment or
leaving the - polarity assignment).