Final Exam Chapter 5

How many 20A, 120V circuits are required for forty-two, 300W incandescent luminaries (noncontinuous load)?

6 circuits

How many 20A, 120V circuits are required for forty-two, 300W luminaries (noncontinuous load) that have a power factor of 85%?

7 circuits

The total opposition to current flow in an AC circuit is called "___________" and is measured in ohms.

impedance

In a purely resistive ac circuit, the current and voltage are _____________. This means that they both reach their zero and peak value 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

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

nonlinear

The magnitude of self induced voltage 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 any useful work. It's the effects that the moving electrons have on the loads they flow through that are important.

true

When alternating current increases, the polarity of the CEMF within the conductor tries to prevent the current from increasing.

true

When describing the relationship between voltage and current, the reference waveform is always _________________.

voltage

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

Xlittlec

Self-induced voltage opposed the change in current flowing in the conductor. This is called "inductive reactance" and is abbreviated _____________.

Xlittlel

The abbreviation for impedance is ________________.

Z

If you measure voltage and current in an inductive or capacitive circuit and then multiply them together, you obtain the circuit's _____________

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

For ac circuits, the ac _____ of a conductor must be taken into consideration.

eddy currents, skin effect, resistance (all of these)

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

false

AC inductive or capacitive reactive loads cause the voltage and current to be in-phase with each other.

false

Because apparent power (VA) is greater than true power (W), more loads can be placed on a circuit, so fewer circuits and panels, and smaller transformers might be required.

false

The true power of an ac circuit equals the volts times the amperes.

false

What does it cost per year (at 9 cents per kWh) for ten 150W recessed luminaries to operate if they are turned on for six hours per day?

$300

If the output is 1,600W and the equipment is 88% efficient, what are the input amperes at 120V?

15A

In a purely inductive circuit, the CEMF waveform is _____________ out-of-phase with the applied voltage waveform

180 degrees

The waveform of the CEMF is ___ out of phase with the applied voltage

180degrees

What size transformer is required for a 100A, 240V, single-phase noncontinuous load (unity power factor?)

25kVA

What size transformer is required for a 100A, 240V, single-phase noncontinuous load that has a power factor of 85 percent?

25kVA

The induced voltage in a conductor carrying alternating current opposed the change in current flowing through the conductor. The induced voltage that opposed the current flow is called "_____________."

CEMF, counter-electromotive force, back-EMF (all of these.)

In dc circuits, the only property that affects voltage and current flow is __________________.

resistance

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

The expanding and collapsing magnetic field within the conductor induces a voltage in the conductors (CEMF) that repels the flowing electrons toward the surface of the conductor. This is called "__________."

skin effect

The effective value is equal to the peak value

times 0.707 and divided by 1.41 (a and c)

The peak value is equal to the effective value _____.

times 1.41

Efficiency describes how much input energy is used for its intended purpose. True or false?

true

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

true