AC/DC Final Exam 1

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

6 circuits

What is the voltage drop of two 12 AWG conductors (total of 0.40 ohms for both conductors) supplying a 16A load, located 100 ft. from the power supply?

6.40 volts

" _______________" is defined as the rate of work measured by the unit called the watt

Power

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 major advantage of ac over dc is the ease of voltage regulation by the use of a transformer

True

The opposition to current flow in a voltage drop of the circuit voltage

True

To determine the resistance of each element in the circuit, the formula R = E squared / P. E is the rated voltage of the resistor, and P is the rated power of the resistor

True

The approximate decimal equivalent for the fraction "4/18" is ________

.2

Distribution transformers reduce the primary distribution voltage to secondary distribution voltage, such as __________

120/208V 120/240V 277/480V

What is the area in sq. in. of trade size 2 raceway?

3 sq. in.

What is the voltage drop of each ungrounded conductor of a 4-wire multiwire circuit? Each conductor is 12 AWG, 100 ft. in length, supplying a 16A load. The resistance of 12 AWG conductors is 2 ohms per 1,000 ft.

3.20V

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

Capacitance

"Normally Closed" means the contacts are closed when the coil is energized

False

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

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

False

Every component of an electrical circuit contains resistance, except the power supply

False

In a parallel circuit, the total circuit resistance is always greater than the smallest resistance

False

In a parallel circuit, the voltage drop across each resistance is equal to the sum of the voltage drops of each of the resistors in parallel

False

The Law of Attraction and Repulsion of magnets states, "Like poles attract and unlike poles oppose each other"

False

The direction of the electromagnetic field around a conductor because of current flow is determined by the right-hand rule as it relates to electron theory

False

The field intensity around a conductor carrying current decreases with increased current flow, and is stronger the further the distance from the conductor

False

The motor FLA rating is used when sizing motor conductors or circuit protection

False

To force electrons to move, some form of energy must be applied to the electrons to cause them to leave their atom. This energy can only be supplied by magnetism.

False

When electricity is created by chemical activity, electrons will flow in two directions. This is called "alternating current"

False

When electrons are forced to move through a conductor, the magnetic fields of individual electrons subtract from one another

False

If two conductive materials in contact with each other are separated, most of the electrons will return to the original surface before the separation is complete

True

Permeability describes the relative ease with which a material can be magnetized

True

That portion of the series-parallel circuit that contains resistances in parallel must comply with the rules for parallel circuits

True

The actual motor current depends upon the load on the motor and the operating voltage at the terminals

True

The attraction between the positive charge of the protons and negative charge of electrons keeps the electrons from breaking out of their orbit

True

The grounded conductor is a conductor that is intentionally grounded to the earth

True

The severity of an electric shock is dependent on the current flowing through the body, which is impacted by circuit voltage and contact resistance

True

When a magnetic field moves through a coil of wire, the lines of flux 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 energy is applied to the valence electrons, the energy is distributed evenly among all the valence electrons

True

When magnetized material keeps its magnetic field for a long time, it is a permanent magnet. Hard iron or steel is used for permanent magnets.

True

When power supplies are connected in parallel, the voltage remains the same, but the current or amp-hour capacity will be increased

True

When working with series-parallel circuits, it is best to redraw the circuit so you can see the series components and the parallel branches

True

What is the approximate output of a 5 hp, 480V, three-phase motor?

3.75kW

Kichoff's Current Law states, "In a series circuit, the current is ________ through the transformer, the conductors, and the appliance"

the same

The electrical system usually begins at the generating plant that converts energy to __________, three-phase power

13.80kV

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

180 degrees

When working any formula, the key to finding the correct answer is to follow what four steps?

Step 1: Know what the question is asking you to find Step 2: Determine the knowns of the circuit Step 3: Select the formula Step 4: Work out the formula

A balanced multiwire branch circuit has current flow only on the ungrounded conductors

True

A series circuit is a circuit in which a specific amount of current leaves the voltage source and flows through every electrical device in a single path before it returns to the voltage source

True

A simple ac generator consists of a loop of wire rotating between the lines of force between the opposite poles of a magnet

True

According to the Electron Current Flow Theory, electrons flow away from the negative terminal of the source, through the circuit and load, toward the positive terminal of the source

True

Compounds can change the electrical characteristics of an individual atom. For example, the insulating aluminum-oxide compound is very difficult to break and it often results in the overheating of aluminum conductors at their terminals

True

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

True

Energy is stored in the electromagnetic field of an inductor and the electric field of a capacitor

True

Fluorescent lighting is illumination that results from the combination of electroluminescence and phosphorescence

True

If a magnetizing force is applied to the end of an iron bar, the magnetic field of many of the ferrous molecule electrons will align with each other and the bar will demonstrate magnetic properties

True

To help reduce the hazard of electrical fires from a parallel arcing fault, the NEC requires a listed AFCI-protection device to protect __________ wiring in dwelling unit bedrooms

branch circuit feeder service

DC motors use brushes with springs to hold them in contact with a(n) ___________

commutator

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

conductive

The formulas in the formula wheel apply to _____________

dc, and ac with unity power

Because of their light weight, ________ actively participate in the transfer of energy.

electrons

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

hertz

Because of the earth's _____________ resistance to current flow, it cannot be used for the purpose of clearing a line-to-case ground fault

high

Lightning is the discharging of _____________________within clouds to each other, to the earth, and sometimes to space

high-voltage cells

The movement of electrons caused by an external magnetic field is called " _______ current", and the associated potential that is established is called "__________ voltage"

induced

____________ breakers operate on the principle of electromagnetism only and are used for very large motors

instantaneous trip

If protection of electrical equipment from lightning is desired, then a ______________________ must be installed on the electrical system in accordance with the NEC.

listed surge-protection device

A thermal-magnetic circuit breaker typically clears fault current in less than 3 to 5 cycles when subjected to a(n) __________

overload or short circuit

The multipoint grounded neutral is intended to reduce the ______________ neutral voltage drop, assist in clearing ___________ line-to-neutral faults, and reduce elevated voltage caused by line-to-ground faults

primary/primary

Ohmmeters measure the _______ or opposition to current flow of a circuit or component

resistance

The Megger is used to measure very high-________ values, such as those found in cable insulation, or motor and transformer windings

resistance

The Wheatstone Bridge meter is used for extremely accurate _________ measurements

resistance

A _______________ is a circuit that contains some resistances in series and some resistances in parallel with each other

series-parallel circuit

To prevent corrosion from forming on low-voltage electronic circuitry connectors, _______ plating is often placed on copper cable terminals

silver, or gold