AC Electricity 1
hertz (Hz)
A unit used for measuring the frequency of vibrations or of AC electricity. It is used for the frequency of any type of repeating cycles of motion. One hertz is equal to one cycle per second. named for Heinrich Hertz, a German physicist.
inductive reactance
An opposition to the flow of AC caused by the generation of an induced voltage whose polarity is opposite to that of the voltage that created it.
alternation
In AC current, one half of an AC cycle in which the voltage or current rises or falls from zero to peak and back to zero.
instantaneous value
In AC electricity, the value found by multiplying the peak value of a sine wave by the sine of the angle through which the loop rotates beyond its zero voltage position.
apparent power
In an AC circuit, the product of RMS (root mean square) current and RMS voltage, expressed in volt amperes.
resistive circuits
In electronics, a circuit constructed entirely of resistive elements (no capacitive or inductive components). In such a circuit, the voltage and current are in phase.
average value
Sine wave alternating current. 0.637 times the peak value of alternating current or voltage, measured from the zero reference line.
peak to peak value
The difference between the positive and negative peak values of an AC sine wave.
left hand rule
The direction of magnetic flux: If the fingers of the left hand encircle a conductor in the direction of the lines of magnetic flux, the thumb will point in the direction of electron flow.
Lenz's law
The law of induced current that says the current induced in a conductor will produce a magnetic field that opposes the field producing the original current.
peak value
The maximum value of AC or voltage measured from the zero reference line.
phase angle
The number of degrees of generator rotation between the time the voltage passes through zero and the time the current passes through zero in the same direction. In AC electricity, the amount of phase shift between the current and voltage.
true power
The power that actually exists in an AC circuit. It is the product of the voltage, current, and power factor; or is the product of the voltage and the current that is in phase with that voltage. True power is expressed in watts.
volt amps
The product of the voltage and current in a circuit.
inductance (L)
The property of an electric conductor or circuit that causes an electromotive force to be generated by a change in the current flowing through it.
power factor
The ratio of the resistance of an electrical circuit to the circuit impedance measured by a wattmeter. In AC electricity, the ratio of apparent power to true power.
effective value
The root mean square (RMS) value of sine wave AC. It is equivalent to .707 times the peak value and corresponds to the DC value that will produce the same amount of heat.
zero degree angle
The starting point at the zero reference line of a sine wave as seen on an oscilloscope measuring the alternation of an AC electrical cycle.
period
The time required for one cycle of AC.
root mean square (RMS)
The value of direct current equivalent to an alternating current sine wave. The value is .707 times the peak value of one alternation.
sine wave
The wave form of alternating current produced by a rotary generator. Its amplitude at any time is proportional to the sine of the angle through which the generator has turned.
counter electromotive force
When alternating current is conducted through a winding, a small current is generated that is 180 degrees out of phase with the primary current. This is a counterelectromotive force (CEMF).
