Current is the rate of flow of electrons per unit time and is measured in amperes (A). An ammeter is used to measure the electric current in a circuit.

A diode allows current to pass easily in one direction and blocks current in the other direction. Diodes are commonly used for rectification which is the conversion of alternating current (AC) into direct current (DC). Because a diode only allows current flow in one direction, it will pass either the upper or lower half of AC waves (half-wave rectification) creating pulsating DC. Multiple diodes can be connected together to utilize both halves of the AC signal in full-wave rectification.

Connecting the 6 batteries in series multiplies their voltage while keeping their current the same yielding a 90V 20A configuration. Connecting the 6 batteries in parallel multiplies their current while keeping their voltage the same yielding a 15V 120A configuration. Using a series-parallel connection, 3 batteries can be connected in series and 3 can be connected in parallel resulting in a 45V 60A configuration.

A series circuit has only one path for current to flow. In a series circuit, current (I) is the same throughout the circuit and is equal to the total voltage (V) applied to the circuit divided by the total resistance (R) of the loads in the circuit. The sum of the voltage drops across each resistor in the circuit will equal the total voltage applied to the circuit.

Capacitors store electricity and are used in circuits as temporary batteries. Capacitors are charged by DC current (AC current passes through a capacitor) and that stored charge can later be dissipated into the circuit as needed. Capacitors are often used to maintain power within a system when it is disconnected from its primary power source or to smooth out or filter voltage within a circuit.