ELECTRICAL PRINCIPLES
ELECTRICAL PRINCIPLES
Capacitance and inductance terminology and units; Radio frequency definition and units; Impedance definition and units; Calculating power
What describes the ability to store energy in an electric field?
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:
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:
"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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What describes the ability to store energy in a magnetic field?
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:
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:
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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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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What does the abbreviation “RF” mean?
RF is "Radio Frequency" - it's not reflected force or any of these other choices. Just learn this one.
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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...
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
What is the formula used to calculate electrical power (P) in a DC circuit?
\[P={E}\times{I}\]
\[E=\frac{P}{I}\]
\[I=\frac{P}{E}\]
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
How much power is delivered by a voltage of 13.8 volts DC and a current of 10 amperes?
\(P = I \times E\) \(=\) \(10 \times 13.8\) \(=\) \(138\) 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
How much power is delivered by a voltage of 12 volts DC and a current of 2.5 amperes?
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 (\(A\)).
\(P = 12V \times 2.5A = 30W\)
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Tags: math dc power electrical power electromotive force (voltage) electrical current power law arrl chapter 3 arrl module 4
How much current is required to deliver 120 watts at a voltage of 12 volts DC?
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
What is impedance?
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."
Read more
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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There is no easy way to remember this, you just have to know your metric abbreviations.
The abbreviation for Hertz is Hz, eliminating all except for kHz. However, on the real test, there may be different choices.
Any metric abbreviation lower than mega, or 1,000,000, is not capitalized, which includes kilo. So, the correct answer choice is kHz. This is useful to know for other Technician Class test questions, just remember that >= 1,000,000 is capitalized, < 1,000,000 isn’t.
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