MH EEP Unit 3 HW

A self-induced voltage waveform, also known as counter-electromotive force (CEMF), is _____ out-of-phase with the applied voltage waveform.

180°

In a purely inductive reactive circuit, the self-induced voltage waveform (CEMF) is _____ out-of-phase with the current waveform and 180° out-of-phase with the applied voltage waveform.

90°

The most significant use of self-induction for industry includes _____.

All of these ( transformers, motors, generators)

"_____" is the ability of a device to store electrical energy and to release that energy.

Capacitance

A simple ac generator can be visualized as a loop of wire rotating within the magnetic lines of force between similar poles of a magnet.

False

A wire's resistance is inversely proportional to its length.

False

The peak value of a waveform is the maximum value the current or voltage waveform reaches during each full cycle of the rotation of the generator's rotor.

False

A "lagging" waveform is when the voltage lags behind the current and a "leading" waveform means the voltage leads the current.

True

A pure direct-current waveform displays the polarity and magnitude of the current or voltage as a flat waveform.

True

A three-phase generator has each of its three windings evenly spaced around the rotor and the windings are 120° out-of-phase from each other.

True

As the frequency at which electromagnetic fields expand and collapse increases, the self-induced voltage within the wire increases.

True

Capacitors are also used to store arc producing energy spikes caused by circuit inductance when switch or relay contacts open under load.

True

Capacitors are often used to smooth out pulsating direct-current waveforms when ac is rectified to dc.

True

Current flow in an alternating-current circuit moves in both directions due to the changing polarity of the voltage, whereas direct current flows only in one direction.

True

Effective current value is also known as the "Root-Mean-Square" (RMS) value.

True

Efficiency describes how much input energy in watts is used for its intended useful purpose and is expressed as a ratio of output power to input power.

True

For a pure resistive load, there's no leading or lagging of the voltage relative to the current. The power factor of the circuit is 100 percent or "Unity."

True

For current to flow through a circuit, the power source must apply enough electromotive force (voltage) to cause electrons to flow.

True

Frequency is expressed as cycles per second, or Hertz (Hz).

True

If a capacitor becomes overcharged, the electrons from the negative metal plate can be pulled through the insulation (dielectric) to the positive metal plate by an excessive electric field.

True

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

True

Root-Mean-Square (RMS) describes the calculation steps (in reverse) necessary to determine the effective ac voltage or ac current value of a waveform.

True

The Formula Wheel is a combination and expansion of the Ohm's Law Formula Circle and Watt's Law.

True

The effective value of ac voltage or ac current is the equivalent value of dc voltage or dc current that would produce the same amount of heat in a resistor.

True

The heating of wires, transformers, and motor windings is wasted energy and is called "power losses."

True

The only thing needed to induce voltage is relative motion between a wire and an electromagnetic field and is the principle that explains how generators and transformers function.

True

The power factor of inductive loads causes the VA load to be greater than the true power (watts).

True

The resistance in a wire is inversely proportional to its cross-sectional area. If the wire's diameter is increased, then its resistance will decrease.

True

The total power consumed in a parallel circuit equals the sum of the powers in each branch.

True

The waveform for alternating-current circuits is symmetrical with positive above and negative below the zero-reference level.

True

True power is always equal to, or less than, apparent power (VA) and is expressed in watts.

True

Waveforms that are "in-phase" with each other means that at every instant, the current is exactly in step with the applied voltage, and both the current and voltage waveforms reach their zero and peak values at the same instant in time.

True

When alternating current is applied to a capacitor, the current continuously moves back and forth charging and discharging the capacitor.

True

The amount of self-induced voltage created within a winding is directly proportional to _____.

all of these ( current flow, the number of wire loops (or turns), frequency at which the expanding and collapsing electromagnetic fields cut through the wires of the winding)

For alternating current, the effective value can be determined by using which of the following formulas?

all of these (Effective Value = RMS Value, Effective Value = Peak Value x 0.707, Effective Value = Peak Value/1.414)

Most commercial alternating-current power is produced by a generator driven by _____.

any of these ( wind, steam, water)

In circuits with _____ loads, the voltage waveform finishes after the current waveform so the voltage "lags" the current.

capacitive

When a _____ has reached its maximum potential difference between its metal plates, it's said to be "charged."

capacitor

To discharge a capacitor, a _____ path is required between its positive (+) and negative (

conductive

A waveform is a mathematical representation on a graph that can be used to visualize the level and direction of _____ in a circuit.

current or voltage

Capacitance is measured in units of _____.

farads

In circuits with _____ loads, the voltage waveform finishes its cycle before the current waveform, so the voltage waveform "leads" the current waveform.

inductive

The electromagnetic field intensity of a coil of wires (winding) carrying alternating current can be increased by inserting a soft _____ core within the wire winding.

iron

A nonsinusoidal (or nonsymmetrical) waveform is produced when multiple alternating-current waveforms of different frequencies are introduced on a circuit, typically by _____.

nonlinear loads

True power is the total energy consumed and is expressed in _____.

watts (P)