Current (I) is the rate of flow of charge, measured in amperes (A). I = Q/t
Potential Difference (p.d.) (V) is the energy transferred per unit of charge, measured in volts (V). V = E/Q
Resistance (R) opposes current flow, measured in ohms (Ω).
Ohm's Law: V = IR — the current through a resistor is proportional to the voltage, provided temperature is constant.
For an ohmic conductor (e.g. resistor at constant temperature), a V-I graph is a straight line through the origin.