Trans(chapters1-4)

A formula that can be used to find the total inductance of parallel inductors is LT = ____.

(L1+L2)/(L1+L2)

In magnetic measurement, ____ lines of flux are equal to one weber (Wb).

100,000,000

For a magnet with an area of 2 square inches and a flux density of 121, what is the pull (in pounds)?

3.361x10"-6

Each time constant in an exponential curve is equal to ____% of some value.

63.2%

In a pure inductive circuit, the current lags the voltage by ____.

90 degrees

The formula for Ohm's Law is ____.

E=IxR

In the ____ system, the term used to describe the total force producing a magnetic field, or flux, is magnetomotive force (mmf).

English

One of the formulas for determining current in a single-phase circuit is ____.

I=VA/E

An electrical measurement called ____ is used to measure the reactive power in a pure inductive circuit.

VAR

According to ANSI rules, the high-voltage leads of a transformer are to be marked H 1 - H 2, and so forth, and the low-voltage leads are marked ____, and so forth.

X1-X2

When a coil is wound around a nonmagnetic material such as wood or plastic, it is known as a(n) ____ magnet.

air core

The polarity of transformer windings can be determined by connecting one lead of the primary to one lead of the secondary and testing for an increase or decrease in voltage. This is often referred to as a ____ connection.

buck or boost

There are actually only three substances that form natural magnets: iron, nickel, and ____

cobalt

The angular difference between true north and magnetic north is known as the angle of ____.

declination

____ materials are either metal or nonmetal materials that cannot be magnetized.

diamagnetic

A device often used to prevent induced voltage spikes when the current flow through an inductor is stopped is the ____.

diode

Magnetic materials contain tiny magnetic structures in their molecular material known as magnetic ____.

domains

Iron-core inductors cannot be used for high-frequency applications because of ____ loss and hysteresis loss in the core material.

eddy current

If the values of all the inductors are the same, total inductance can be found by using the following formula: L T = N / L.

false

The important factors concerning magnetic induction are a magnetic field, movement, and polarity.

false

The primary winding of a transformer is the side of the transformer that is connected to the driven load.

false

The reason that the isolation transformer can greatly increase any voltage spikes before they reach the secondary is because of the rise time of current through an inductor.

false

There will always be some amount of current flow in the primary of any voltage transformer even if there is no load connected to the secondary. This is called the relaxation current of the transformer.

false

Viability is a measure of a material's willingness to become magnetized.

false

When inductors are connected in series, the total inductance of the circuit (L T) equals the sum of the inductances of all the inductors divided by the number of inductors.

false

____ will demagnetize an object.

heating

A coil has an inductance of one ____ when a current change of one ampere per second results in an induced voltage of one volt.

henry

The amount of ____ voltage in an inductor can be computed if the resistance of the wire in the coil and the amount of circuit current are known.

induced

____ is an induced voltage and is, therefore, proportional to the three factors that determine induced voltage.

inductive reactance

The polarity of an electromagnet can be determined using the ____ rule

left hand rule

The ____ transformer is basically an isolation transformer with a high-voltage rating on the primary winding, and that is intended for use in metering circuits.

potential

The amount of core material needed for a particular transformer is determined by the ____ rating of the transformer.

power

When a resistive load is suddenly connected to a source of direct current, the current will instantly ____.

rise to maximum value

____ occurs when all the molecules of the magnetic material are lined up.

saturation

A(n) ____ diode has a forward voltage drop of approximately 0.7 V regardless of the current flowing through it.

silicon

Three factors determine the amount of voltage that will be induced in a conductor: the number of turns of wire, the strength of the magnetic field (flux density), and the ____ of the cutting action.

speed

A basic law concerning transformers is that all values of a transformer are proportional to its turns ratio.

true

Almost all transformer nameplates will list the primary voltage, secondary voltage, and kVA rating.

true

Assume an inductor with a negligible resistance is connected to a 36-V, 400-Hz line. If the circuit has a current flow of 0.2 A, the inductance of the inductor is 0.0716 H.

true

Because they are always able to align themselves north and south, natural magnets became known as "leading stones" or lodestones.

true

Magnetic lines of flux repel each other and never cross.

true

Since induced voltage is always in opposition to applied voltage, the applied voltage must overcome the induced voltage before current can flow through the circuit.

true

The induced voltage is proportional to the rate of change of current (speed of the cutting action).

true

The polarity of the induced voltage is determined by the polarity of the magnetic field in relation to the direction of movement.

true

The schematic symbol used to represent an inductor depicts a coil of wire.

true

When an object is to be demagnetized, its molecules must be disarranged as they are in a non-magnetized material.

true

When the primary of a transformer is connected to power but there is no load connected to the secondary, current is limited by the inductive reactance of the primary.

true

The exponential curve can often be found in nature.

truesp

The two factors that determine the number of flux lines produced by an electromagnet are the number of ____ and the amount of current flow through the wire.

turns of wire

A(n) ____ occurs when the current flow through an inductor stops, and the current decreases at an exponential rate also.

voltage spike

An inductor has an inductance of 0.8 H and is connected to a 120-V, 60-Hz line. How much current will flow in this circuit if the wire resistance of the inductor is negligible?

.398A

Three inductors are connected in parallel. Inductor 1 has an inductance of 2.5 H, inductor 2 has an inductance of 1.8 H, and inductor 3 has an inductance of 1.2 H. The total inductance of this circuit is ____H.

.559H

Three inductors are connected in series. Inductor 1 has an inductance of 0.6 H, inductor 2 has an inductance of 0.4 H, and inductor 3 has an inductance of 0.5 H. The total inductance of the circuit is ____ H.

1.5H

Assume that an isolation transformer has 240 turns of wire on the primary and 60 turns of wire on the secondary. This is a ratio of 4:1 (240/60 = 4). Now assume that 120 V is connected to the primary winding. The voltage of the secondary winding is ____V.

30 Volts

A basic law of magnetism states that like poles attract and unlike poles repel.(T&F)

false

A common type of isolation transformer found throughout industry is the control transformer, which is used to increase the line voltage to the value needed to operate control circuits.

false

A device that uses the collapsing magnetic field of an inductor to produce a very low voltage is the electric-fence charger.

false

A good rule for any type of transformer is that power in is always slightly greater than power out.

false

A speaker uses three separate magnets. One is a permanent magnet, and two are electromagnets.(T&F)

false

Energy is required to create a magnetic field, and energy is required to maintain a magnetic field.

false

Flux density is measured in lines per square centimeter.

false

If a conductor cuts magnetic lines of flux at a rate of 1 V, a voltage of 1 Wb/s will be induced.

false

In a pure inductive circuit, the true power, or wattage, is equal to the product of the voltage and current. In a pure resistive circuit, however, no true power is produced.

false

Inductance is measured in units called the henry and is represented by the letter H.

false

Reactance is caused by inductance, so it is called reactive inductance.

false

Residual magnetism is a measure of a material's ability to retain magnetism.

false

Some amount of inductance is present in all alternating-current circuits because the magnetic field does not change.

false

The exponential curve describes a rate of certain occurrences and is divided into four time constants.

false

The time necessary for current in an inductor to reach its full Ohm's law value, called the R-L time constant, can be computed using the formula L = H / R.

false

A very common type of isolation transformer is the distribution transformer, which is used to supply power to ____.

homes and business

The principle of magnetic ____ states that whenever a conductor cuts through magnetic lines of flux, a voltage is induced into the conductor.

induction

Transformers can be divided into several classifications, which include ____.

isolation,auto and current

A basic law of physics states that whenever an electric current flows through a conductor, a magnetic field is formed around the conductor.

true

A device that can be used for spike suppression in either direct- or alternating-current circuits is the metal oxide varistor (MOV).

true

A total current-limiting effect is called impedance and is symbolized by the letter Z.

true

Factors such as the amount and type of core material, wire size used to construct the windings, number of turns, and the degree of magnetic coupling between the windings greatly affect the transformer's impedance.

true

The amount of induced voltage in an inductor can be computed if the resistance of the wire in the coil and the amount of circuit current are known.

true

The amount of inrush current in the primary of a transformer is limited by amount of applied voltage, resistance of the wire in the primary winding, and flux change of the magnetic field in the core.

true

A transformer nameplate does not list the current rating of the windings. The current rating for a winding can be determined by dividing the kVA rating by the ____.

winding voltage

The current-limiting property of the inductor is called reactance and is symbolized by the letter ____.

x