Unit 16,17,18,19

A three-phase generator has each of its windings out-of-phase with each other by________.

120 degrees

Ina purely inductive circuit the CEMF waveform is ______ our of phase with the applied voltage waveform.

180 degrees

The waveform is the comfiest is_____ out-of-phase wit the applied voltage

180 degrees

In an inductive circuit, the CEMF waveform is 90 degrees out of phase with the current waveform and 180 out of phase with the applied voltage waveform making the voltage waveform lead the current waveform

90 degrees

If you measure voltage and current in an inductive or capacitive circuit and then multiply them together, you obtain the circuits________.

Apparent power

Self-induced voltage is 180 degrees out-of-phase with the ______. When the applied voltage is at its maximum in one direction, the induced voltage is at its maximum in the opposite direction

Applied voltage

"_________" is a property of an electrical circuit that enables it to store electrical energy by means of an electric field and to release energy at a later time

Capacitance

When a capacitor has a potential difference between the plates it is said to be ______. One plate has an excess of free electrons, and the other plate has a lack of them.

Charged

To discharge a capacitor all that is required is a(n) ________ path between terminals of the capacitor. The free electrons on the negative plate then flow through the external circuit to the positive plate.

Conductive

A half-wave recitifier can be used to convert ac voltage into dc voltage to continuously charge a capacitor

False

A waveform image is used to display the level and direction of current , but not voltage

False

Ac inductive or capacitive reactive loads cause the voltage and current to be in-phase with eachother

False

Because apparent power(va) is greater than true power (w) more kids can be placed on a circuit, so fewer circuits and panels and smaller transformers might be required

False

Conductor resistance is directly proportional to the conductors length and cross- sectional area

False

Eddy currents are small independent currents induced within the conductor because of direct current

False

The true power of an ac circuit equals volta times amperes

False

The number of complete waveforms in one second is called the "frequency ". Frequency is expressed as "__________" or "cycles per second"

Hertz

Ina purely resistive ac circuit the current and voltage are _____. This means that they both reach their zero and peak values at the same time

In-phase

The movement of electrons caused by an external magnetic field is called"__________current" and the associated potential that is established is called________ voltage.

Induced

"______" is the value of the voltage or current at a moment of time.

Instantaneous

When the current waveform finishes before the voltage waveform the voltage"_______"the current waveform.

Lags

The voltage waveform finished before the current waveform, the voltage is said to "________" the current waveform

Lead

A capacitor is a device that resist changed in current because a capacitor introduces reactance to the circuit, it shifts the current waveform to __________.

Lead the applied voltage by 90 degrees

The direction of the overall magnetic field around the conductor follows the __________ rule based on the electron current flow theory

Left-hand

A common practical use of induction is for _________.

Motors Generators Transformers

A nonsinusoidal waveform is created when ________ loads distort the voltage and current sine wave

Nonlinear

The combination of alternating-current and direct- current waveforms results in a ________ waveform

Nonsymmetrical

The output voltage of a generator depends upon the

Number of turns of wire Strength of the magnetic field Soeed at which the coil rotates

When an ac circuit supplies power to a purely_____ loaf the circuit voltage and current are in-phase with eachother. This condition is called "unity power factor "

Resistive

"________" describes the steps necessary to determine the effective voltage or current value

Root-mean-square

As the alternating current through a conductor increases, an expanding and collapsing electromagnetic field through the conductor induces a voltage within the conductor. This is known as"_______ voltage".

Self-induced

If a capacitor is overcharged the electrons from the negative plate can be pulled through th e insulation to the positive plate. The capacitor is then said to have_____.

Shorted

The explaining and collapsing magnetic field within the conductor indices a voltage in the conductors (cemf) that repels the flowing electrons toward the surface of the conductor. This is called"______".

Skin effect

The peak value is equal to the effective value ________.

Times 1.41

Alternating current is primarily used because it can be transmitted inexpensively

True

Because an iron core provides an easy path for magnetic flux, windings with a soft iron cores produce a greater self-inductance than windings with air cores.

True

Effective ac voltage or effective ac current that would produce the same amount of heat in a resistor.

True

Even when power is removed from the circuit, capacitors can store large amounts of energy for a long period of time and can discharge or arc if inadvertently shorted or grounded out

True

In ac generators that produce large quantities of electricity the conductor coils are stationary and the magnetic field revolves within the coils

True

Power factor is a measurement of how far the current is out-of-phase with the voltage

True

The magnitude of self-induced voltage within within a winding is directly proportional to the current flow the winding and the frequency at which magnetic fields cut through the winding

True

The movement of electrons themselves does not produce useful work. It's the effects that the moving electrons have on the loads they flow through that are important

True

The waveform of ac circuits display the level and direction of the current and voltage for every instant of time for one full revolution of the rotor

True

When a magnetic field moves through a coil of wire the lines of force of the magnetic field cause the electrons in the wire to flow in a specific direction. When the magnetic field moves in the opposite direction, electrons in the wire flow in the opposite direction

True

When alternating current decreases the polarity of the induced voltage within the conductor tries to prevent the current from decreasing

True

When electrons move the magnetic fields of the individual electrons combine to produce an overall magnetic field. The greater the current flow, the greater the overall magnetic field around the conductor

True

Self inductance voltage oppresses the change in current flowing in the conductor. This is called"inductive reactance" and it is abbreviated_________.

XL

The opposition offered to the flow of alternating current by a capacitor is called capacitive reactance. Is expressed in ohms and abbreviated

Xc