AC Theory Midterm

Counter-electromotive force (CEMF) is _______ (how many) degrees out of phase with the applied voltage?

180

what Is peak voltage of rms voltage is 240v

339.3 v

in ac generation, as a conductor is directly under the north pole, it is cueing max lines of Flux at

90 degrees of rotation

the basic rule is that inductors always oppose a change in

AC current

which type of generator uses slip rings and brushes

AC revolving armature generator

if we multiply the voltage total and current total, we would get a value of the hypotenuse of the power triangle, which would be the total apparent power. measured in Volt-Amperes.

Apparent Power.

the instaneous voltage can be found by

Epeak= Einst x .707

effective value of an AC sine wave is also called

RMS voltage

it is in volt-amperes reactive, and is not consumed power but rather stored power that is returned as the magnetic fields dissipate.

Reactive Power.

describe the RMS value of a voltage

Root mean square or RMS is because its the value of the AC waveform that has peaks and valleys but RMS has the same heating effect as a DC voltage of the same value

What is the difference between a revolving armature ac generator and a revolving field ac generator?

The revolving armature uses slip rings instead of a commutator, which the rings connect directly to the armature windings to the load. The revolving field ac generator allows the magnetic field to spin and the coils of wire where voltage is induced to remain still. Which because of this means having slip rings is redundant in this generator build

inductance is measured in Henries

True

the watts dissipated by the resistor will be the current through the resistor times the voltage drop across the resistor. using p= Ix E we can find the solution to true power.

True Power

What can be done to shift current and voltage back into phase in a circuit with poor power factor?

a capacitor can be put in place to move current back in phase with voltage to give it a better power factor correction

What is an inductor?

a coil of wire wrapped around a core

to induce a voltage, what three things are necessary

a conductor, magnetic field, and relative motion

what is inductance?

a current carrying conductor coil or circuit to induce a voltage into itself or adjacent circuits

to determine the actual amount of degrees that the voltage and current are "out of phase" you must find

angle theta

If current stops flowing in a conductor, the magnetic field will....

begin to diminish to zero

How can angle theta be used to determine your power factor for a circuit?

by taking the cosine of the angle theta multiplied by 100. This works because the cosine is the ratio given by dividing the adjacent side of the power triangle by the hypotenuse of the power triangle.

List 3 ways that we can increase the magnetic field from an electromagnet.

coil the wire tighter, bigger wire to be used for the coil electromagnet, add a core of ferromagnetic material to the coil

magnetic fields around a _____ as current flows through it

conductor

Describe how electrical conductors are different from insulators.

conductors have one or two valence electrons, so its easier to move as energy is added to the mix. Less valence electrons the better for conductors. Insulators are good for breaking down electrical flow as it has more valence electrons, around 6-8.

CEMF stand for

counter electro- motive force

on a purely inductive circuit, _______ by 90 electrical degrees

current lags voltage

As current decreases, the magnetic field that is produced

decreases

If current is observed. in the circuit, to flow from the negative side of a power supply, to the positive side of a power supply, this is an example of ______________ current flow.

electron current flow

The magnetic field produced from an AC signal applied to a conductor will _________________

expand and collapse

List the 6 sources of electrical energy listed in the Chapter #1 reading

friction chemical heat pressure light magnetism

The intensity of the magnetic field that is produced from an electromagnet depends on two factors. List the two factors.

how tightly wound the coil is, and how my current is flowing through

total opposition to the current is

impedance

if you increase frequency of a supply voltage what happens to inductive reactance

increases

an electromagnetic strength is increased

increasing number of turns in a coil

the formula for XL=2(3.14)(F)(L) what does L represent

inductance of the coil

the inductor produces a back voltage and acts as an opposition to the applied current . this is measured in ohms called

inductive reactance

Which of the following metals is the best material to design an inductor core from?

iron

how does a core help inductance

it helps her more lines of flux and have a growing magnetic field

Describe Lenz's Law.

it states that an induced voltage or current opposes the motion that created the induced voltage or current.

If a customer were to ask you to describe power factor correction, what would you tell them?

its to try to lower the amount of reactive power in the circuit, the main goal is to make the energy drawn by the load to be more efficient. Power factor correction is all about trying to bring voltage and current closer in phase with one another, to give you a better power factor, and make the energy bill cheaper. Capacitors are common ways to implement a fix for power factor correction.

Inductors store energy in the form of a __________ ___________.

magnetic field

Whenever current flows through a conductor, the movement of electrons produces a __________ _________ around the material.

magnetic field

Anytime current flows in a conductor a ________ _________ is produced. Because of the resistance in the wire _______ is also produced.

magnetic field, current

Conductors have magnetic fields produced as current flows through them. If a conductor is moved through a magnetic field, a difference of electical potential will be developed between the ends of the conductor. This is called _____________ ____________.

magnetic induction

When the current changes direction, the magnetic field it produced changes ....

magnetic polarity

does DC circuits experience inductance reactance

no, since the DC circuit is steady

List the 4 physical properties of that affect inductance

number of turns of wire, spacing between the turns, cross sectional area of the core, and permeability of the core material

The ability of a material to concentrate or focus magnetic flux lines is called ____

permeability

Lines of magnetic flux are the most dense at the ________ of the magnet.

poles

vertical diagrams at used to plot opposition to cent flow which opposition is plotted on horizontal axis

resistance

what does RMS stand for

root mean square

As current flows through a coil of wire a magnetic field is produced in each "turn" of wire. These magnetic fields cut through the neighboring turns and a small voltage is produced internal to the coil. This phenomenon is called _________ ___________.

self inductance

electrical component to induce a voltage into itself as through the current component changes called

self inductance

The inductive effect is NOT noted when a magnetic field is:

stationary

The formula for determining the exact speed a generator must spin at to produce a desired frequency is called __________ ___________

synchronous speed

inductance

the ability of a current carrying coil to induce a voltage into itself

Give 2 examples of where electromagnets may be used.

the big magnets that grab cars at scrapyards, and also in generators it's used

If a difference in potential is produced between the ends of a conductor, and the conductor is arranged in a complete circuit, what will happen?

the current flows

Anytime a conductor is moved through a magnetic field ________ is induced in the conductor and if there is a complete circuit _______ will flow.

voltage, current