Terms  Definitions 

Alternating current can be defined as current that varies in 
1. amplitude and direction

Before a 120volt dc source can be used to power a 12volt load, the voltage must be reduced. Which of the following methods can be used? 1. A resistor placed in parallel with the load 2. A resistor placed in series with the load 3. A stepdown transforme 
2. A resistor placed in series with the load

Alternating current has replaced direct current in modern transmission systems because it has what advantage? 
4. Ac can be readily stepped up or down

A waveform is a graphic plot of what quantities? 
2. Amplitude versus time

Which of the following properties surrounds a currentcarrying conductor? 1. A magnetic field 2. A repulsive force 3. An attractive force 4. An electrostatic field 
1. A magnetic field

What statement accurately describes the magnetic field surrounding a currentcarrying conductor? 
It is perpendicular to and equal along all parts of the conductor

When you grasp a coil in your left hand with your thumb pointing in the direction of the north pole, your fingers will be wrapped around the coil in the direction of the 
current flow

The power consumed in a conductor in realigning the atoms which set up the magnetic field is known as what type of loss? 
Hysteresis loss

The magnetic field surrounding a straight conductor is (a) what shape, and (b) is in what position relative to the conductor? 
(a) Concentric circles
(b) Perpendicular 
Why is a twopole magnetic field set up around a coil? 
Because separate lines of magnetic force link and combine their effects

When a conductor is moving parallel to magnetic lines of force, (a) what relative number of magnetic lines are cut, and (b) what relative value of emf is induced? 
(a) Minimum
(b) Minimum 
When the induced voltage in a conductor rotating in a magnetic field is plotted against the degrees of rotation, the plot will take what shape? 
A sine curve

When a loop of wire is rotated through 360º in a magnetic field, the induced voltage will be zero at what point? 
180º

When a loop of wire is rotated 360º in a magnetic field, at what points will the induced voltage reach its maximum (a) positive, and (b) negative values? 
(a) 90º
(b) 270º 
When a coil of wire makes eight complete revolutions through a single magnetic field, (a) what total number of alternations of voltage will be generated and, (b) what total number of cycles of ac will be generated? 
(a) 16
(b) 8 
According to the lefthand rule for generators, when your thumb points in the direction of rotation, your (a) forefinger and (b) your middle finger will indicate the relative directions of what quantities? 
(a) Magnetic flux, north to south,
(b) Current 
Continuous rotation of a conductor through magnetic lines of force will produce what type of (a) voltage and (b) waveform? 
(a) AC
(b) Sine Wave 
What is the term for the number of complete cycles of ac produced in one second? 
Frequency

What is the unit of measurement for frequency? 
Hertz

A loop of wire rotating at 60 rpm in a magnetic field will produce an ac voltage of what frequency? 
1 HZ

An ac voltage has a frequency of 350 Hz. In two seconds, what total number of times will the peak value of voltage be generated? 
1400 times

The value of current of an ac waveform taken at any particular moment of time is what type of value? 
Instantaneous value

While the value of an ac voltage may be expressed as one of several values, the accepted practice is to express it as what type value? 
Effective value

The total of ten instantaneous values of an alternation divided by ten is equal to what value? 
The average value

What mathematical formula is used to find the average value of voltage for an ac voltage? 
Eavg = 0.636 X Emax

The value of alternating current that will heat a resistor to the same temperature as an equal value of direct current is known as 
Ieff

The rms value for an ac voltage is equal to what other ac value? 
Eavg

What value will result by squaring all values for Einst, averaging these values, and then taking the square root of that average? 
Eeff

An ac voltmeter is usually calibrated to read what AC value? 
Effective

If the maximum value for an ac voltage is known, the Eeff can be found by using which of the following formulas? 
Eeff = Emax X .707

What is an important rule to remember when using Ohm's Law to solve ac circuit problems? 
Never mix values

The property of inductance offers opposition to what quantitie? 
Changes in current

What is the unit of measurement for inductance? 
Henry

What physical property is similar to inductance? 
Inertia

The difference in potential across a resistor, created by current through the resistor is an example of what force? 
Electromotive

When a magnetic field moves through a stationary conductor, the electrons in orbit are affected in what manner? 
They are dislodged from orbit

When electrons are moved in a conductor by a magnetic field, a force known by what term is created? 
Electromotive

Selfinduced emf is also known as what force? 
Counter electromotive force

According to Lenz’s Law, the induced emf produced by a change in current in an inductive circuit tends to have what effect on the current? 
It opposes either a rise or a fall in current

The direction of the induced voltage in an inductor may be found by application of what rule? 
The lefthand rule for generators

When source voltage is removed from a currentcarrying conductor, a voltage will be induced in the conductor by what action? 
The collapsing magnetic field

How are inductors classified? 
By core type

Normally, most coils have cores composed of either air or 
soft iron

The hollow form of nonmagnetic material found in the center of an aircore coil has what purpose? 
To support the windings

Why do large diameter coils have greater inductance than smaller diameter coils, all other factors being the same? 
Large diameter coils have more wire and thus more flux

If the radius of a coil is doubled, its inductance is increased by what factor? 
Four

If the length of a coil is doubled while the number of turns is kept the same, this will have (a) what effect on inductance and (b) by what factor? 
(a) Decrease
(b) by 1/2 
A soft iron core will increase inductance because it has what characteristics? 
High permeability and low
reluctance 
An increase in the permeability of the core of a coil will increase what coil characteristic? 
Magnetic flux

If a coil is wound in layers, its inductance will be greater than that of a similar singlelayer coil because of a higher (what) 
Flux linkage

Regardless of the method used, inductance of a coil can ONLY be increased by increasing what coil characteristic? 
Flux linkage

What does the Greek letter Delta signify as in "ΔI" or "Δt"? 
The values are changing

Inductors experience copper loss for what reason? 
Because the reactance of an inductor is greater than the resistance of an inductor

What term applies to the power loss in an iron core inductor due to the current induced in the core? 
Eddycurrent loss

Power consumed by an iron core inductor in reversing the magnetic field of the core is termed as what type of loss? 
Hysteresis loss

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