AC Fundamentals 241

AC

Alternating current. Current that reverses direction at regularly recurring intervals of time. AC usually alternates 60 times per second, or 60 hertz, in the U.S.

active power

The result of both current and voltage reaching their peaks simultaneously. Active power, also called true power, is a measurement of the rate at which electricity performs work such as producing heat, light, or mechanical energy.

alternating current

AC. Current that reverses direction at regularly recurring intervals of time. Alternating current usually alternates 60 times per second, or 60 hertz, in the U.S.

alternator

A device that generates AC. Alternators produce this current through the use of a mechanical device such as an engine or a motor.

amp

A unit of measurement that indicates the amount of current flowing in a circuit. Amp is short for ampere.

amplitude

A measurement of the size of a wave. Amplitude is also referred to as magnitude.

amplitude

A measurement of the size of a wave. Amplitude measures the intensity of a signal.

angle of rotation

The position and direction of the circular motion that is used to produce voltage in a sine wave. The angle of rotation affects electrical variables.

apparent power

The combination of both true power and reactive power. Apparent power is the product of voltage in an AC circuit multiplied by all current flowing through the circuit system.

armature

A device found in generators that has many separate coils wound around it. An armature rotates in the generator and creates a magnetic field that produces direct current.

average value

The mean value of all of the AC values during one AC cycle. Average value is a result of the RMS value.

battery

A device that converts chemical energy to electrical energy. Batteries are a source of DC.

capacitive load

An AC electrical load in which the current wave reaches its peak before the voltage wave. Capacitive load values can be calculated using the impedance formula.

capacitive reactance

The opposition in the capacitor to voltage changes. The value of capacitive reactance is required to calculate impedance in an AC circuit.

capacitor

C. A device that stores current. Capacitors release current when it is needed in a circuit.

cathode-ray oscilloscope

CRO. The earliest analog-based oscilloscope. Cathode-ray oscilloscopes do not always display waves in a traditional representation, requiring users to do more work to interpret their readings.

circuit

A completely enclosed path of electrical current consisting of various devices. Electrical circuits usually include a source, path, load, and control.

conductor

A wire that allows for the easy flow of electricity. Conductors move in a magnetic field and produce voltage.

constants

A value, factor, or number that does not change. In AC circuits, impedance is a constant.

cycles

One complete revolution or rotation. In AC, a cycle is considered to be a completed 360° waveform.

cyclical

Charactertized by repetitive action. One complete AC cycle is 360 electrical degrees.

DC

Direct current. Current that flows in one direction. Direct current does not reverse the direction of flow.

degrees

Units of measurement for angles and circular motion. Degrees express the amount of rotation in a sine wave.

digital storage oscilloscopes

DSO. A device that produces a digital visual display of a voltage or current wave shape. Digital oscilloscopes are more commonly used than analog versions because they require less interpretation by users.

direct current

DC. Current that flows in one direction. Direct current is the less common form of current.

effective value

An AC value that is given as the equivalent of a DC value. An effective value is the value that AC would have to produce to have the same effect as a DC value.

efficiency

A measure of the energy output of a system versus the total energy supplied to it. Maximum efficiency is achieved with a linear load.

electric current

The flow or movement of charged particles. Electric current can flow in two different ways within a circuit.

electrical degrees

Units of measurement for expressing the amount of rotation in a generator. Electrical degrees describe the position in an AC sine wave.

electromagnetic induction

The process in which current is generated by a magnetic field using a current-carrying coil. Electromagnetic induction produces current in an AC generator.

electrons

A negatively charged particle that orbits the nucleus of an atom. Electrons flow between atoms to cause electricity.

frequency

A measurement of the number of complete AC cycles that occur in one second. Frequency is measured in hertz (Hz).

generator

A device that converts mechanical energy into electrical energy by magnetic induction. Generators create AC power and sine waves.

hertz

Hz. A unit of measurement indicating a single cycle in an alternating current. Sixty Hz is the most common frequency for a given electrical outlet in the U.S.

impedance

Z. A measure of reactance and resistance in an AC circuit. Impedance is calculated to measure the total opposition to current flow in an AC circuit.

in phase

The state in which current and voltage reach their peaks at the same time in alternating current. When current and voltage are in phase, true power occurs.

inductive load

An AC electrical load in which the voltage wave reaches its peak before the current wave. Inductive load values can be calculated using the impedance formula.

inductive reactance

The opposition in the inductor to current flow. The value of inductive reactance is required to calculate impedance in an AC circuit.

inductor

L. A device that opposes changes in current flow. Inductors store energy as a magnetic field.

LC circuits

A type of AC circuit that includes a power source that is connected to an inductor and a capacitor. LC circuits can be used to tune radio stations.

linear load

An AC electrical load in which both current and voltage waves reach their peak simultaneously. Linear loads are necessary to achieve maximum efficiency.

linear wave

A waveform that is graphically represented with straight lines. The voltage of a linear wave rises at a constant rate with time.

load

A component in a circuit that converts electricity into light, heat, or mechanical motion. Loads may include light bulbs, appliances, or machines.

magnetic field

A force of attraction that surrounds magnets and current-carrying conductors. Magnetic fields cause electromagnetic induction.

magnetic flux

The force that surrounds a magnet and exhibits the powers of attraction and repulsion. Magnetic flux is described as imaginary lines of force that exit the magnet's north pole and return to its south pole.

magnitude

A measurement of the size of a wave. Magnitude is also referred to as amplitude.

magnitude

The size of a wave. Magnitude is the highest positive point on the wave and the maximum positive voltage value.

negative peak value

The lowest negative point on a wave. Negative peak value is equal to the lowest voltage of the wave.

ohm

A unit of measurement of electrical resistance. Ohms multiplied by amperes equals volts as stated by Ohm's law.

Ohm's law

The law describing the relationship between amperage, voltage, and resistance. Ohm's law states that volts equals amperes multiplied by ohms.

oscillators

Devices that produce a continuous string of on/off pulses at a preset frequency. Oscillators produce square waves.

oscilloscope

A device that produces a visual trace of a voltage or current wave shape. Oscilloscopes are used to view AC and DC waves graphically.

peak

The highest amplitude value on a wave. The peak of a wave can be negative or positive.

peak amplitude

The highest amplitude value on a wave. Peak amplitude can be negative or positive.

peak negative voltage

The lowest negative point on a wave. Peak negative voltage indicates the maximum negative pressure of the wave.

peak positive voltage

The highest positive point on a wave. Peak positive voltage indicates the maximum positive pressure of the wave.

peak-to-peak value

A measurement from the negative peak value to the positive peak value. Peak-to-peak value is determined by adding the positive peak amplitude to the negative peak amplitude.

period

The reciprocal value of frequency. A period measures the amount of time for one cycle to be completed.

phase angle

A measurement that is used to represent the inefficiency in an AC circuit. The phase angle is used on the power triangle to explain the relationship between the different types of AC power.

polarity

A state of opposites. Polarity involves the north and south attractions of a magnet and the positive and negative changes in a circuit.

pole

Either of two oppositely charged ends of a magnet. The relationship of the poles causes magnetic flux.

positive peak value

The highest positive point on a wave. Positive peak value is equal to the highest voltage of the wave.

power

The amount of work accomplished within a given period of time. Power is the product of current and voltage and is measured in watts.

power supply

A device that provides DC power to a circuit. Power supplies often must convert AC to DC.

power triangle

A graphic representation of the relationship between the three different types of AC power and the phase angle. The power triangle is used to calculate total power in a circuit.

RC circuits

A type of AC circuit that includes a power source connected to a resistor and a capacitor. RC circuits can be used as filters for current.

reactance

X. A measure of how difficult it is for current to move through an inductor. Reactance is a factor when calculating impedance in an AC circuit.

reactive power

Power that is required to produce magnetic fields. Reactive power is often described as stored power because it does not produce work.

reciprocal

The inverse of a given value. A reciprocal is equal to 1 divided by the number.

resistance

A measure of how difficult it is for current to move through a conductor. Resistance is a factor when calculating impedance in an AC circuit.

resistor

R. A device that restricts current flow. Resistors produce work, such as heat, light, or mechanical motion.

RL circuits

A type of AC circuit that includes a power source that is connected to a resistor and an inductor. RL circuits can be used as DC power supplies.

RLC circuits

A type of AC circuit that includes a power source connected to a resistor,an inductor, and a capacitor. RLC circuits are used to tune radios and audio receivers.

root mean square

RMS. The effective value of AC. RMS is the value that AC would have to produce to have the same effect as a DC value and is determined using the RMS formula.

root mean square formula

The formula used to determine the effective value of an AC sine wave. RMS is equal to the peak value multiplied by 0.707.

sawtooth wave

A type of AC waveform that is produced by electronic test devices. Sawtooth waves rise and fall in straight lines.

sine

In a right triangle, the ratio of the side opposite an angle to the longest side of the triangle. In AC, the voltage of a sine wave is equal to the peak voltage multiplied by the sine of the angle of rotation.

sine

SIN. The ratio of the length of the opposite side to the length of the longest side of a right triangle. The sine of the angle of rotation is used to find the voltage of a sine wave.

sine function

The act of determining the ratio of the length of the opposite side to the length of the longest side of a right triangle. The sine function is used to find the voltage of a sine wave.

sine wave

The most common type of AC waveform. Sine waves consist of 360 electrical degrees and are produced by rotating machines.

sine waves

The most common type of AC waveform. A sine wave consists of 360 electrical degrees.

slip ring

A conductive device attached to the end of a generator rotor that conducts current to the brushes. Slips rings are also used in AC wound rotor motors.

square wave

AC waveforms that have squared peaks. Square waves are produced by oscillators.

stepped down

A phrase used to describe voltage adjustment in electricity. When voltage is stepped down, it has been decreased.

stepped up

A phrase used to describe voltage adjustment in electricity. When voltage is stepped up, it has been increased.

test probe

A device attached to a measuring instrument. Test probes send the electrical signal being measured to the oscilloscope.

total power

The full amount of power in an AC circuit. Total power takes into account true power, reactive power, and apparent power.

transformers

A device that transfers electrical energy from one circuit to another without changing the frequency. Transformers are most often used to change line voltage.

triangle wave

A type of AC waveform that appears as repeating triangles. The voltage for a triangle wave rises and falls at a constant rate.

trigonometry

The branch of mathematics that addresses the measurements and relationships of a triangle and its parts. AC circuit calculations require knowledge of trigonometry.

trigonometry

The branch of mathematics that addresses the measurements and relationships of a triangle and its parts. Knowledge of trigonometry is required to make AC circuit calculations.

true power

The result of both current and voltage reaching their peaks simultaneously. True power, also called active power, is a measurement of the rate at which electricity performs work such as producing heat, light, or mechanical energy.

variables

Factors in electricity that change according to the situation. Variables in AC circuits include voltage, current, and resistance.

volt

A unit of measurement that indicates the amount of electromagnetic force, also called pressure, in a circuit. Volts measure voltage.

voltage

A measure of electrical pressure or potential known as electromotive force. Voltage is measured in volts.

voltage drops

The amount of energy used by a device with resistance in the circuit. Voltage drops are experienced with both AC and DC.

volt-amperes

VA. A unit of electrical power that measures apparent power. Volt-amperes are equal to the product of a single volt and a single ampere.

volt-amperes reactive

VAR. A unit of electrical power that measures reactive power. Volt-amperes reactive is the product of the apparent power multiplied by the sine of the phase angle between voltage and current.

volts

A measure of electrical pressure or potential known as electromotive force. Volts measure voltage.

watts

A unit of measurement that indicates the amount of electrical power present in a circuit or device. Watts require a change in energy to exist.

waveforms

The type or shape of wave produced by AC. Waveforms depend upon the angle at which a rotating armature cuts through lines of magnetic flux.

wavelengths

The distance between separate peaks of a sine wave. AC produces wavelengths of both current and voltage.

waves

A graphic representation of the flow of alternating current. Wave shapes depend on the method by which the current is produced.

work

The result of electricity flowing through resistance. Work appears in the form of heat, light, or mechanical energy or motion.