Ohm's Law
A complete circuit must have an unbroken path so I (current) can flow out of the battery V (Voltage Source), through the resistor R (Load) connected to it, and back into the battery. If a connection is removed at any point, the circuit is broken, or Open (Open Circuit).
The relationship between the values of I, V and R is known as Ohm's Law:
The current (I) flowing in a circuit is directly proportional to the applied voltage (V) and inversely proportional to the resistance (R) it is going through.
Current
I gives the value of the current when the voltage and resistance are known.
I quantity is expressed in amperes (A)
Voltage
V gives the value of the voltage when the current and the resistance are known.
V quantity is expressed in volts (V)
Note In many cases V is represented by ε = EMF (ElectroMagnetic Force) or V is represented by U (volts).
Resistance
R gives the value of the resistance when the current and the voltage are known.
R quantity is expressed in ohms (Ω)
Conductance is the inverse of the resistance.
in Siemens.