A rectifier is a component that uses diodes to force current to flow in a single direction. Different modes of rectification produce slightly different waveforms, but all of them take an alternating input and output a direct (pulsating) current. For example, instead of the waveform varying from +140 to 0 to -140 and back, the rectified output varies from +140 to 0 to +140 to 0, with all current flowing in the same direction (the actual voltages are just an example).

A transformer changes the voltage level of a signal (for example from 5 V to 10 V or from 110 V to 12 V). An amplifier increases the magnitude of a signal. A reflector is part of an antenna and is not an electronic circuit that converts AC to DC.

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A relay is an electrically‑controlled switch. It uses a small electrical current to energize an electromagnet (the relay coil) which physically moves contacts to open or close a separate circuit that can carry much higher current or voltage. Relays are commonly used in vehicles and other equipment where a low‑power control signal needs to switch a higher‑power load.

For more detail, see: http://en.wikipedia.org/wiki/Relay

Memory aids:

• A relay lets a low‑power control signal operate a high‑power circuit (think: small coil current operates a big switch).
• Example: a relay coil might need ~100 mA to switch contacts rated for 10 A.

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A layer of metal enveloping a wire functions as a Faraday cage, which prevents (or at least attenuates) radio-frequency energy being radiated to or from the wire. This shielding minimizes coupling of unwanted signals to or from the conductor, reducing interference to adjacent wiring or equipment and helping preserve the integrity of the signal carried by the shielded wire.

Shielding is about electromagnetic isolation; it does not change the inherent DC resistance of the conductor nor its current-carrying capacity.

Memory aids:

• Think "shielded" = "shield" = blocks RF (Faraday cage).
• Shielding prevents coupling of unwanted signals to/from the wire.

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A meter is a device that measures an electrical quantity and presents the result on a numeric scale or display. Common examples include voltmeters, ammeters, ohmmeters, and signal strength meters — all of which give a numeric reading of the quantity being measured.

A potentiometer is a variable resistor, a transistor is a semiconductor device used for switching or amplification, and a relay is an electrically operated switch. Those components affect or control the flow of current but do not themselves display an electrical quantity as a numeric value.

Memory aids:

• Meter: measures and shows a numeric value (voltmeter, ammeter, ohmmeter, signal-strength meter).
• Potentiometer: variable resistor (adjusts voltage/limit current).
• Transistor: switch/amplifier (controls current flow electronically).
• Relay: electrically controlled switch (uses an electromagnet to open/close contacts).

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A regulator, often called a voltage regulator, controls (regulates) the output voltage of a power supply so that it stays at a desired level. The exact output voltage and how much current can be supplied depend on the regulator type and any other components in the circuit.

The other circuit types listed do not perform this voltage-control function:

• oscillator — generates an electrical signal (usually a periodic waveform)
• filter — performs signal processing by removing or emphasizing frequency components
• phase inverter — produces two outputs: one identical to the input and one that is phase-inverted (a mirror image)

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A "Transformer" is made up of two inductive coils wound around a ferrite core. The primary coil is connected to the voltage source and the secondary coil is connected to the circuit you are powering. The ratio of the number of turns on the primary coil to the secondary coil determines the output voltage.

For example, a 20 : 5 transformer fed 120 V AC will produce 30 V AC on the secondary coil.

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LED stands for Light Emitting Diode. It is a type of diode (which conducts current primarily in one direction) that produces light when current flows through it, so it is commonly used as a visual indicator. LEDs also tend to have much lower power consumption and longer life than traditional incandescent indicator lamps, which makes them a practical choice for panel indicators, status lights, and similar uses.

Memory aids:

• LED = Light Emitting Diode
• LEDs produce light and use less power than incandescent bulbs

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A "tuned circuit" (resonant circuit) is formed by an inductor (L) and a capacitor (C). These two components exchange energy back and forth — the capacitor stores energy in its electric field and the inductor stores energy in its magnetic field — producing oscillations at the circuit's resonant frequency. Such a circuit is commonly called an LC circuit.

The "L" designation for inductance is historically associated with Lenz (as in Lenz's law), who studied induced currents and magnetic effects.

Memory aids:

• "C, I Tuned it." Capacitor + Inductor = Tuned (resonant) circuit.

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An integrated circuit (IC), commonly called a microchip, is a single packaged device that contains multiple semiconductor devices (such as transistors and diodes) and other components (like resistors and capacitors) interconnected to perform one or more electronic functions. The components are fabricated together on a small piece of semiconductor material and then enclosed in a package so the whole assembly can be used as a single component. Examples range from simple logic chips to complex CPUs and memory devices; nearly every modern circuit board includes ICs.

Memory aids:

• (none)

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Resonance in an electrical circuit happens when the inductive reactance and the capacitive reactance are equal in magnitude but opposite in phase at a particular frequency. When that condition is met the circuit is said to be "tuned" to that frequency and will either pass (series resonance) or reject (parallel resonance) signals near that frequency. An inductor and a capacitor connected in series or in parallel form such a tuned (resonant) circuit.

The other items listed are not resonant circuits: a linear voltage regulator controls DC voltage, a resistor network used to reduce SWR is just resistive (it does not produce inductive/capacitive reactance that cancels), and a circuit described only as high-fidelity audio refers to audio quality rather than a specific LC resonance.

Memory aids (if any):

• L + C = tuned/resonant circuit (inductor + capacitor)

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