Alternating current and Transformers
The property of inductance is present in which of following electrical circuits?
*An ac circuit *a dc circuit *a resistive circuit
Which factors determines the intersity of a magnetic field surrounding a coil?
*The amount of current flow through the coil *The type of core material *The number of turns in the conductor
Which of the following properties surronds a current-carrying conductor?
A magnetic field
before a 120-volt dc source can be used to power 12-volt load, the voltage must be reduced. Which of the following methods can be used?
A resistor placed in series with the load
Alternating current has replaced direct current in modern transmission systems because it has what advantages?
AC can be readily stepped up or down
A waveform is a graphic plot of what quantities?
Amplitude versus time
Electrostatic fields have what effect on free electrons and bound electrons?
Attracts them to the negative charges and distorts their orbits
capacitance and inductance in a circuit are similar in which of the following ways?
Both cause the storage of energy
How are inductors classified?
By core type
How are fixedd caparcitors classified?
By their dielectric materials
Which of the following factors will NOT affect the value of inductance of a coil?
Conductor tensility
What is the symbol used to denote the basic unit of measurement for inductance?
H
What is the unit of measurement for inductance?
Henry
What is the unit of measurement for inductane?
Henry
What is the unit of measurement for frequency?
Hertz
A soft iron core will increase inductance because it has whawt characteristic?
High permeability and low reluctance
Power consumed by an iron core inductor in reversing the magnetic field of the core is termed as what type of loss?
Hysteresis loss
The power consumed in a conductor in realigning the atoms which set up the magnetic field is known as what type of loss?
Hyteresis loss
The value of current of an AC waveform taken at any particular moment of time is what type of value?
Instantaneous value
Which of the following statements accurately describes the magnetic field surrounding a current-carrying conductor?
It is perpendicular to and equal along all parts of the conductor
Which of the following types of capacitors are referred to as self-healing?
Oil
Electrostatic lines of force radiate from a charged particle along what type of lines?
Straight lines
The direction of the induced voltage in an inductor may be found by application of which of the following rules?
The left-hand rule for generators
The coefficient of coupling between two coils is a measure of what factor?
The magnetic flux ratio linking the coils
Which of the following actions will increase the capacitance of a capacitor?
The plates are moved closer together
When a magnetic field moves through a stationary conductor, the electrons in orbit are affected in what manner?
They are dislodge from orbit
What type of dielectric is LEAST sensitive to power dielectric-hysteresis losses?
Vacuum
Two capacitors are indentical with the exception of the material used for the dielectric. Which of the following combinations of dielectric materials will cause the capacitors to have almost the same capacitance?
Vacuum, air
When does mutual inductance occurs between inductors?
Whenever the effect of one inductor is aided by another inductor
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
Two capacitors are identical with the exeption of the material used for the dielectric. Which of the following combinations of dielectric material will cause capacitor(b) to have a larger capacitance than capacitor(a)?
a. Glycerine b. Pure water
The magnetic field surrounding a straight conductor is(a)what shape, and (b) in in what position relative to the conductor?
a.Concentric circles b.Perpendicular
The maximum voltage that can be applied to a capacitor without causing current flow through the diectric is called
working voltage
One L/R time constant is equal to the time required for the current in an inductor to reach what portion of its maximum value?
63.2%
Inductors experience copper loss for what reason?
Because all inductors have resistance which dissipates power
The property of inductance offers opposition to which of the following quantities?
Changes in current
Self-induced emf is also known as what force?
Counter electromotive force
What may cause a capacitor to suffer power losses?
Dielectric hyteresis
Rapid reversals in the polarity of the line voltage applied to a capacitor will cause what type of capacitor power loss?
Dielectric-hysteresis
As the current through a capacitor increases, which of the following types of capacitor losses will increase?
Dielectric-leakage
What term applies to the power loss in an iron core inductore due to the current induced in the core?
Eddy-Current loss
The difference in potential across a resistor, created by current through the resistor is an example of which of the following forces?
Electromotive
A capacitor is a device that stores energy in a/an
Electrostatic Field
Maximum current will flow in an LR circuit after a minimum of how many time constants have elapsed?
Five
If a coild is wound in layers, its inductance will be greater than that of a similar-layer coil because of a higher
Flux linkage
If the radius of a coil is doubled, its inductance is increased by what factor?
Four
When the number of turns is increased in a coil from 2 to 4, the total inductance will increase by a factor of
Four
What is the symbol for inductance?
L
Mutual inductance between two coils is affected by which of the following factors?
Material of the windings?
Alternatin current can be defined as current that varies in
amplitude and direction
The left hand rule for generators states that the thumb of the left hand points in the direction of motion 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
What physical property is similar to inductance?
inertia
Capacitance is defined as the property of a circuit that
opposes a change in voltage
When electrons are moved in a conductor by a magnetic field, a force known by which term?
poterntial difference
Normally, most coils have cores composed of either air or
soft iron
The hollow form of nonmagnetic material found in the center of an air core coil has what purpose?
to support the windings
