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Subelement T5
Electrical principles: math for electronics; electronic principles; Ohm's Law
Section T5C
Electronic principles: capacitance; inductance; current flow in circuits; alternating current; definition of RF; DC power calculations; impedance
What is the ability to store energy in an electric field called?
  • Inductance
  • Resistance
  • Tolerance
  • Capacitance

This one can throw people off a bit; in 2 years of tracking statistics on tests, nobody has chosen B or C for this question, but many confuse Inductance and Capacitance, which are pretty similar on this question.

A capacitor is a passive component that consists of at least one pair of conductors separated by a dielectric (an insulator). When voltage is applied to the capacitor (creating a difference in potential between the two) it creates an electric field across the dielectric which stores energy. The easiest way for me to remember these is that an inductor, being a coil of wire, is used to create an electromagnet (you can make an electromagnet by wrapping a coil of insulated wire around a nail, for example), and so an inductor stores energy in a magnetic field. The capacitor stores energy in an electric field.

Once again:

What is the ability to store energy in a MAGNETIC field called? Inductance

What is the ability to store energy in an ELECTRIC field called? Capacitance

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Tags: electronics definitions capacitance arrl chapter 3 arrl module 6

What is the basic unit of capacitance?
  • The farad
  • The ohm
  • The volt
  • The henry

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

The other units listed here are:

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Tags: electronics definitions capacitance arrl chapter 3 arrl module 6

What is the ability to store energy in a magnetic field called?
  • Admittance
  • Capacitance
  • Resistance
  • Inductance

An inductor is a coil of wire, usually around a non-ferrite (nonmagnetic) core. The basic unit of inductance is the henry. Whenever you make a coil of wire, it creates a magnetic field; think of an electromagnet, which is basically an inductor with a ferrite core. The ability to store energy in such a field is Inductance. So remember -- inductance creates a magnetic field.

Capacitance has a very similar (and in fact opposite) effect to an inductor and creates an electric field.

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Tags: electronics definitions inductance arrl chapter 3 arrl module 6

What is the basic unit of inductance?
  • The coulomb
  • The farad
  • The henry
  • The ohm

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.

The other (incorrect) answers here are:

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Tags: electronics definitions inductance arrl chapter 3 arrl module 6

What is the unit of frequency?
  • Hertz
  • Henry
  • Farad
  • Tesla

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 clock ticks at \(1\)Hz. The wall outlet AC 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

What does the abbreviation "RF" refer to?
  • Radio frequency signals of all types
  • The resonant frequency of a tuned circuit
  • The real frequency transmitted as opposed to the apparent frequency
  • Reflective force in antenna transmission lines

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

What is a usual name for electromagnetic waves that travel through space?
  • Gravity waves
  • Sound waves
  • Radio waves
  • Pressure waves

Electromagnetic waves are radio waves. Radio waves are typically denoted by electromagnetic wavelengths longer then Infrared. As with all electromagnetic waves, they travel at the speed of light.

The other wrong options:

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Tags: radio waves definitions arrl chapter 4 arrl module 9

What is the formula used to calculate electrical power in a DC circuit?
  • Power (P) equals voltage (E) multiplied by current (I)
  • Power (P) equals voltage (E) divided by current (I)
  • Power (P) equals voltage (E) minus current (I)
  • Power (P) equals voltage (E) plus current (I)

\(P={E}\times{I}\)

\(E=\frac{P}{I}\)

\(I=\frac{P}{E}\)

  • P for Power (Watt)
  • E for Electromotive Force (Voltage) (Volt)
  • I for Intensity (Current) (Ampere)

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Tags: formulas math electrical power electrical current electromotive force (voltage) power law arrl chapter 3 arrl module 5

How much power is being used in a circuit when the applied voltage is 13.8 volts DC and the current is 10 amperes?
  • 138 watts
  • 0.7 watts
  • 23.8 watts
  • 3.8 watts

\(P = I \times E\) \(=\) \(10 \times 13.8\) \(=\) \(138\) 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 5

How much power is being used in a circuit when the applied voltage is 12 volts DC and the current is 2.5 amperes?
  • 4.8 watts
  • 30 watts
  • 14.5 watts
  • 0.208 watts

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 5

How many amperes are flowing in a circuit when the applied voltage is 12 volts DC and the load is 120 watts?
  • 0.1 amperes
  • 10 amperes
  • 12 amperes
  • 132 amperes

\(P = I \times E\)

\(I = \frac{P}{E}\) \(=\) \(\frac{120}{12}\) \(=\) \(10\) amperes

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Tags: math ohm's law electrical current electrical power arrl chapter 3 arrl module 5

What is meant by the term impedance?
  • It is a measure of the opposition to AC current flow in a circuit
  • It is the inverse of resistance
  • It is a measure of the Q or Quality Factor of a component
  • It is a measure of the power handling capability of a component

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."

Impedance, incidentally, is measured in Ohms.

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Tags: arrl chapter 3 arrl module 6

What are the units of impedance?
  • Volts
  • Amperes
  • Coulombs
  • Ohms

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 6

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