Semiconductors have valence shells that are exacly half full and can conduct electricity under some conditions but not others. This property makes them useful for the control of electrical current.

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.

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.

Ohm's law specifies the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit: V = IR.

Solved for resistance, R = \( \frac{V}{I} \) = \( \frac{120}{1.5} \) = 80 Ω

A transformer utilizes an inductor to increase or decrease the voltage in a circuit. AC flowing in a coil wrapped around an iron core magnetizes the core causing it to produce a magnetic field. This magnetic field generates a voltage in a nearby coil of wire and, depending on the number of turns in the wire of the primary (source) and secondary coils and their proximity, voltage is induced in the secondary coil.