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Technician Class (Expires Jul 1, 2018)
Subelement T5
Electrical principles: math for electronics; electronic principles; Ohm's Law
Section T5A
Electrical principles, units, and terms: current and voltage; conductors and insulators; alternating and direct current
Electrical current is measured in which of the following units?
• Volts
• Watts
• Ohms
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 4

Electrical power is measured in which of the following units?
• Volts
Watts
• Ohms
• Amperes

Volts - Electromotive force.

Watt-hours - energy

Watts - power.

Amperes - Current.

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Tags: electronics electrical power definitions arrl chapter 3 arrl module 5

What is the name for the flow of electrons in an electric circuit?
• Voltage
• Resistance
• Capacitance
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 4

What is the name for a current that flows only in one direction?
• Alternating current
Direct current
• Normal current
• Smooth current ~

Current that flows only in one direction is found primarily in circuits that use batteries as a power source; Cars, handheld devices, etc. There is a positive and a negative. This is referred to as Direct Current, or DC.

Compare that with the electricity and current in your house, which alternates directions -- Alternating Current. There is a "Hot" and a "Neutral", but Neutral is essentially just the ground that the electricity can flow to; the current alternates in a sine wave from negative to positive.

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

What is the electrical term for the electromotive force (EMF) that causes electron flow?
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.

An easy way to remember why voltage is the correct answer is by using the water analogy: think of voltage as the pressure pushing the water thru the pipe.

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Tags: definitions electromotive force (voltage) electronics arrl chapter 3 arrl module 4

How much voltage does a mobile transceiver usually require?

Car batteries are about $12$ volts (technically they are closer to $13.8$ volts), and since mobile transceivers are most commonly used in a car they are designed to run at about that. This is really convenient, because that means that if you get batteries for running your radio you can charge them by running your car.

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Tags: radio operation dc power arrl chapter 5 arrl module 12

Which of the following is a good electrical conductor?
• Glass
• Wood
Copper
• Rubber

As a general rule of thumb, metal tends to be a good conductor. Water can be (though technically it's the minerals in the water that makes it a good conductor -- salt water is a really good conductor, whereas distilled water is a fair insulator). Most other things, and definitely glass, wood, and rubber, are insulators -- meaning that they don't conduct electricity.

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Tags: electronics electrical components arrl chapter 3 arrl module 4

Which of the following is a good electrical insulator?
• Copper
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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Tags: electronics electrical components arrl chapter 3 arrl module 4

What is the name for a current that reverses direction on a regular basis?
Alternating current
• Direct current
• Circular current
• Vertical current

There are two types of current that you need to worry about. The kind in your house is called Alternating Current, because the current alternates (reverses) direction over time (60 times per second in the US, or 60 Hz; that's 60 times that it goes from positive to negative and back). The RMS (Root Mean Square) voltage of AC in the US is 110 volts, and we use that because it can be sent over longer distances with less loss than the other type, Direct Current.

The most common use of Direct Current, which always goes the same direction, is circuits powered by a battery, such as a car. Battery systems vary in voltage, but most often in Ham Radio (and in cars) they are 12 volts.

The other two options listed here are just to throw you off.

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Tags: ac power electrical current electronics arrl chapter 3 arrl module 4

Which term describes the rate at which electrical energy is used?
• Resistance
• Current
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 multiplied by Voltage.

If you use a water flow analogy, Current (I) is like water volume Flow-rate (liters per second), Voltage (E) is like total Pressure loss along the water pipe (Newtons/square meter or Pa). Resistance (R) is inversely related to the pipe diameter - larger pipe diameter equals less resistance, like a thicker wire does. Mechanical power is then proportional to pressure loss times flow-rate ( Newton meters per second or Watts). So, Power is a RATE of Energy usage.
Power x Time = Energy ( N*m or Watt-seconds). Then, Energy is like the total water volume (liters) moved against a specified pressure loss in a specified time.

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 5

What is the basic unit of electromotive force?
The volt
• The watt
• The ampere
• The ohm

One way to think about electricity in general is the comparison to a water pipe.

Volts = The pressure (e.g. how much "force" does the river have). Also known as the electromotive force. How much the electron wants to move in the wire.

Amps = how much water is actually flowing through the pipe. Number of electrons moving at once.

Watts = The total amount of usable water energy the pipe contains.

Thus, as long as you know any two of these items (Amps, Volts, or Watts), you can figure out the third:

\begin{align} \text{Volts} &= \frac{\text{Watts}}{\text{Amps}}\\ \\ \text{Amps} &= \frac{\text{Watts}}{\text{Volts}}\\ \\ \text{Watts} &= \text{Volts} \times \text{Amps}\\ \end{align}

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Tags: electromotive force (voltage) definitions electronics arrl chapter 3 arrl module 4

What term describes the number of times per second that an alternating current reverses direction?
• Pulse rate
• Speed
• Wavelength