A capacitor is a passive component made of two conductive plates separated by an insulator (called a dielectric). When voltage is applied across the plates, it creates an electric field in the dielectric — and this field stores energy. The property that describes this ability is called capacitance.

So remember:
Capacitance = ability to store energy in an electric field

This is often confused with inductance, which is the ability to store energy in a magnetic field. Both are ways of storing energy, but they work differently.

To help keep them straight:

• Capacitance → stores energy in an electric field
• Inductance → stores energy in a magnetic field

A helpful acronym: MICE
Magnetic → Inductance
Capacitance → Electric

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Tags: electronics definitions capacitance arrl chapter 3 arrl module 5

The basic unit of capacitance, the Farad, is named for the physicist Michael Faraday.

The other units listed here are:

• the Volt - basic unit of voltage
• the Ohm - basic unit of resistance
• the Henry - basic unit of inductance

"Henry was Inducted into the hall of fame, and Faraday tipped his Cap(acitance)."

An additional memory aid: Many of us have heard of a Faraday Cage. Cages CAPture things (CAPacitance)

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Tags: electronics definitions capacitance arrl chapter 3 arrl module 5

An inductor is a passive electronic component made by coiling wire — often around a core, which may be magnetic (like ferrite) or non-magnetic (like air), depending on the application. When current flows through the coil, it creates a magnetic field around it — and that magnetic field stores energy. The property that describes this ability to store energy in a magnetic field is called inductance.

This is a very common source of confusion:
Many people mix up inductance and capacitance because both refer to storing energy — but they store it in different types of fields.

To help keep them straight:

• Inductance → stores energy in a magnetic field
• Capacitance → stores energy in an electric field

A helpful acronym: MICE
Magnetic → Inductance
Capacitance → Electric

So for this question, the ability to store energy in a magnetic field is called inductance.

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Tags: electronics definitions inductance arrl chapter 3 arrl module 5

An inductor is a passive electrical component that stores energy in a magnetic field; its unit is the henry, which is named for Joseph Henry.

It's good to know what the other units listed are as well, since they are all real units:

• the coulomb - unit of electric charge
• the farad - unit of capacitance
• the ohm - unit of resistance

Study Tip: Consider using the line "Henry was inducted into the hall of fame, and (Farad)ay tipped his Cap(acitance)" to jog your memory.

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Tags: electronics definitions inductance arrl chapter 3 arrl module 5

Hertz is the standard unit for frequency, as used in the SI unit system. It is defined as the number of cycles per second of something periodic. For example a quartz clock ticks at \(1\)Hz. The wall outlet AC (in the US) is set to \(60\)Hz. The tone of A just below middle C is \(220\) Hz. The unit is named after Heinrich Hertz](wiki/Heinrich_Hertz). Here is a graphical example from Wikipedia.

The other (incorrect) answers here are:

• the farad - unit of capacitance
• the henry - unit of inductance
• the tesla - unit of magnetic field strength. \(31 µT\) (\(3.1 \times 10 − 5 T\)) - strength of Earth's magnetic field at 0° latitude (on the equator)

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Tags: frequencies definitions arrl chapter 2 arrl module 2

RF is "Radio Frequency" - it's not reflected force or any of these other choices. Just learn this one.

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Tags: arrl chapter 2 arrl module 2

Radio waves are a type of electromagnetic (EM) radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz to as low as 3 kHz, though some definitions describe waves above 1 or 3 GHz as microwaves, or include waves of any lower frequency. (Wikipedia)

EM waves are made up of magnetic field and electric field oscillations in phase with each other, but their direction is perpendicular.

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Tags: arrl chapter 4 arrl module 8

\[P={E}\times{I}\]

\[E=\frac{P}{I}\]

\[I=\frac{P}{E}\]

• P for Power (Watts)
• E for Electromotive Force (Voltage, Volts)
• I for Intensity (Current) (Amperes, Amps)

An easy way to remember is "Pixie". P I x E

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Tags: formulas math electrical power electrical current electromotive force (voltage) power law arrl chapter 3 arrl module 4

\(P = I \times E\) \(=\) \(10 \times 13.8\) \(=\) \(138\) watts

The formula for electrical power is \(P = I \times E\).

"Power (in watts) equals Current (in amperes) multiplied by Potential Energy (in volts)."

\(P\) (watts) = \(10\) (amps)\(\times 13.8\) (volts)

\(10 \times 13.8 = 138\)

\(138\) watts

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Tags: math dc power electrical power electromotive force (voltage) electrical current power law arrl chapter 3 arrl module 4

Power is the rate of of electrical energy generation or consumption.

\(P = V \times I\) (watts \(=\) volts \(\times\) amperes)

Where \(P\) is power (\(W\)), \(V\) is voltage (\(V\)), and \(I\) is current (\(A\)).

• \(P = I \times V\)
• \(V = 12V\)
• \(I = 2.5A\)

\(P = 12V \times 2.5A = 30W\)

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Tags: math dc power electrical power electromotive force (voltage) electrical current power law arrl chapter 3 arrl module 4

We will use the Power Law, which is most commonly written as:

\[P = I \times E\]

We are given:

\(\begin{align} \text{(Power) } P &= 120\text{ watts}\\ \text{(Current) } I &= \text{?}\\ \text{(Voltage) } E &= 12\text{ volts}\\ \end{align}\)

To solve for \(I\) we can divide both sides by \(E\) and get

\(\begin{align} I &= \frac{P}{E}\\ I &= \frac{120}{12}\\ &= 10\text{ amperes} \end{align}\)

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Tags: math ohm's law electrical current electrical power arrl chapter 3 arrl module 4

The inverse of resistance is conductance (the measure is the Mho - can you see how this is related to Ohm?). So that's not the answer.

The measure of \(Q\) is something covered on the General and Extra exams - it's too deep for the Technician exam. So that's not the answer.

Power handling capability? Power is measured in Watts, so the power handling capability would be measured in Watts. Components are certainly rated in things like Watts and Volts and even Amps, but none of those things are called impedance. So that's not the answer.

And that leaves "It is a measure of the opposition to AC current flow in a circuit."

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Impedance, incidentally, is measured in Ohms, and is represented by the symbol Z. For DC systems, impedance and resistance are the same. In AC circuits, impedance possesses both magnitude and phase and is represented by a complex number.

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Tags: arrl chapter 3 arrl module 5

Impedance is actually very similar to resistance in many ways -- which makes sense, since impede and resist are roughly synonymous. Thus it makes sense that they share the same unit -- Ohms.

The main difference between resistance and impedance is that impedance changes with frequency. Inductors pass direct current (frequency of \(0\)) but have a higher impedance the higher the frequency, since inductors tend to resist changes in current. Capacitors have infinite impedance with DC and the higher the frequency the lower the impedance (capacitors resist changes in voltage).

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Tags: arrl chapter 3 arrl module 5

M is the SI abbreviation for mega, indicating millions or \[\times10^6\] Hz is the SI unit abbreviation for Hertz or cycles per second.

Therefore the proper abbreviation for megahertz is...

MHz

Hopefully you will find this easy to remember as you will be seeing it a lot.

Visually, you might also notice that MHz is made up of all straight lines.

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Tags: arrl chapter 2 arrl module 2