This experiment investigates the interrelationships of three basic electrical quantities, current, voltage and resistance.

• Current (I) is the amount of charge (Q) flowing through the cross-sectional surface per unit time. It has units of amperes. In SI units, charge is the coulomb, 1 ampere = 1 coulomb/second. The direction of conventional current is that of positive charge carriers.
• Voltage (V) or the potential difference between any two points is the work needed to move a unit charge from the first point to the second. Potential difference has units of volts. 1 volt = 1 joule/coulomb.
• Resistance (R) of a conductor is defined as the ratio of the potential difference across the conductor (usually an applied voltage) to the current which flows through the conductor. Resistance is measured in units of ohms (W ).

If the resistance is independent of the voltage then the conductor is said to obey Ohm's Law, and the relation between voltage and current is linear. On the other hand, a device whose resistance depends on voltage, R = R(V), is said to be non-Ohmic.

Two rules by Gustav Kirchhoff play an important role in studying circuits.

Kirchhoff's first rule says the current flowing into a junction must equal the current leaving the junction  If charge is conserved (and is not accumulating anywhere, as in a purely resistive circuit), then the charge flowing into a junction (or joining of conductors) must be equal to the charge flowing out of the junction.

Kirchhoff's second rule says that the electric potential energy at any point in a circuit can have only one value at a given time. This means that voltage change or potential difference around any loop (or path which leads from a point and back to it) must be zero.