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Subelement T5
ELECTRICAL PRINCIPLES
Section T5A
Current and voltage: terminology and units, conductors and insulators, alternating and direct current
Electrical current is measured in which of the following units?
• Volts
• Watts
• Ohms
• Correct Answer
Amperes

Volts (Voltage) - Electromotive force, or potential.

Ohms - resistance

Watts - power

Amperes - Current

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Tags: electronics electrical current definitions arrl chapter 3 arrl module 3

Electrical power is measured in which of the following units?
• Volts
• Correct Answer
Watts
• Watt-hours
• Amperes

Volts - Electromotive force.

Ohms - resistance.

Watts - power.

Amperes - Current.

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Tags: electronics electrical power definitions arrl chapter 3 arrl module 4

What is the name for the flow of electrons in an electric circuit?
• Voltage
• Resistance
• Capacitance
• Correct Answer
Current

Think of this in terms of water; what do you call the flow of water? Current.

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Tags: definitions electrical current electronics arrl chapter 3 arrl module 3

What are the units of electrical resistance?
• Siemens
• Mhos
• Correct Answer
Ohms
• Coulombs

This is basic electrical knowledge. Siemens are the SI Unit of electrical conductance, susceptance, and admittance. Mhos are no longer used, and were replaced as the unit of conductance by the Siemens. Coloumbs are the SI unit of electrical charge, leaving Ohms, the SI Unit of resistance, denoted by the Greek symbol Omega, Ω.

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What is the electrical term for the force that causes electron flow?
• Correct Answer
Voltage
• Ampere-hours
• Capacitance
• Inductance

Hard to add to what is already in this question, except possibly to explain what the incorrect questions actually mean. Voltage, of course, is the electrical term for the Electromotive force that causes electron flow.

Capacitance refers to the ability to store energy in a capacitor, which will then oppose a change in voltage. Inductance refers to the ability to store energy in a coil of wire, which will then oppose a change in current. Ampere-hours is a term used to indicate the capacity of a battery -- a 50 ampere-hour battery should be able to provide 1 amp for 50 hours, or 50 amps for 1 hour.

Obviously, none of these other answers could refer to Electromotive Force.

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Tags: definitions electromotive force (voltage) electronics arrl chapter 3 arrl module 3

What is the unit of frequency?
• Correct Answer
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 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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Why are metals generally good conductors of electricity?
• They have relatively high density
• Correct Answer
They have many free electrons
• They have many free protons
• All these choices are correct

Most metals have loosely coupled electrons in the orbit of the atoms. That makes it easier for the electrons to flow from one atom to the next. These electrons are generally thought of as a cloud in the metal structure. Because of this electron cloud, current flows quite easily in most metals.

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Which of the following is a good electrical insulator?
• Copper
• Correct Answer
Glass
• Aluminum
• Mercury

Most metals are good conductors; all of them conduct electricity to some extent. A conductor is something that electricity can flow through. An insulator is the opposite -- something that electricity either doesn't flow through or doesn't flow through very well.

On a ham radio test they aren't going to try to trick you by caring how good of a conductor it is, so if it's looking for a conductor look for something metallic; if it's looking for a insulator, look for something that isn't metallic. In this case, glass is the only item listed that isn't a metal, so it's the insulator.

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Which of the following describes alternating current?
• Current that alternates between a positive direction and zero
• Current that alternates between a negative direction and zero
• Correct Answer
Current that alternates between positive and negative directions
• All these answers are correct

Alternating Current -- or AC -- is the way that commercial and residential power works where the direction of the current alternates between positive and negative at a given frequency (or hz). In the United States the most common form of AC alternates 60 times a second (60Hz) between -120V and +120V. In many other parts of the world it runs at 50Hz between -240v and +240v.

Just remember that the current alternates in direction -- 0V would be no power flow, so zero to positive or zero to negative would be alternating on and off, not alternating direction.

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Which term describes the rate at which electrical energy is used?
• Resistance
• Current
• Correct Answer
Power
• Voltage

Power, also known as "watts", is equal to Voltage times Current ($P=E \times I$). In other words, Power is the product of the electric current at a specified amount of electromotive force. If you use a water analogy, Current could be seen as the diameter of the hose, where voltage is the amount of force available to push it through. Power would be the actual amount of water that gets through the pipe. If you want more water to go through the pipe, you can either apply more force (voltage) or make the pipe bigger (current).

Resistance is the opposition to the current flow, so it definitely could not be considered a viable answer.

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Tags: definitions electronics electrical power arrl chapter 3 arrl module 4

What type of current flow is opposed by resistance?
• Direct current
• Alternating current
• RF current
• Correct Answer
All these choices are correct

Resistance opposes things, and currents are no exception. Any current, electrical or radio, that passes through a resistor will be met with opposition.

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What describes the number of times per second that an alternating current makes a complete cycle?
• Pulse rate
• Speed
• Wavelength
• Correct Answer
Frequency

Just remember, the "Frequency" determines how "frequently" the current reverses direction.

Another way to remember is to analyze the units of each term: Pulse rate (beats per second), Speed (meters per second), Wavelength (meter), Frequency (times per second, or Hz)

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