Basic Electrical Concepts Practice Questions — Armed Services Vocational Aptitude Battery (ASVAB) — Page 7

Question 121Question →

An industrial temperature sensor module with a calibrated internal resistance of $4.5\text{ k}\Omega$ draws a steady direct current of $8\text{ mA}$ during normal operation. What is the voltage drop across the sensor module in volts ( $\text{V}$ )?

Show answer & explanation

Answer: 36

Answer

The voltage drop across the sensor module is

36\text{ V}

.

According to Ohm's Law, voltage (

V

) equals current (

I

) multiplied by resistance (

R

). Given

I = 8\text{ mA} = 0.008\text{ A}

and

R = 4.5\text{ k}\Omega = 4500\text{ }\Omega

, the calculation is

V = 0.008\text{ A} \times 4500\text{ }\Omega = 36\text{ V}

.

Step-by-Step Solution

1

Convert the given metric prefixes to standard base units (amperes and ohms).

I = 8\text{ mA} = 8 \times 10^{-3}\text{ A} = 0.008\text{ A}

and

R = 4.5\text{ k}\Omega = 4.5 \times 10^{3}\text{ }\Omega = 4500\text{ }\Omega

Ohm's law requires fundamental SI units (volts, amperes, and ohms) for accurate mathematical evaluation.

2

Select the appropriate form of Ohm's Law to calculate voltage (

V

).

V = I \times R

Voltage across a resistive load equals the product of the current flowing through it and its resistance.

3

Substitute the converted values into the formula and solve.

V = 0.008\text{ A} \times 4500\text{ }\Omega = 36\text{ V}

Multiplying

8 \times 10^{-3}\text{ A}

by

4.5 \times 10^{3}\text{ }\Omega

simplifies directly to

8 \times 4.5 = 36\text{ V}

because the metric prefixes milli (

10^{-3}

) and kilo (

10^{3}

) cancel each other.

Key Concept

Ohm's Law: Voltage Calculation (

V = I \times R

)

Alternative Method

Recognize that the prefix multiplier milli- (

10^{-3}

) and kilo- (

10^{3}

) cancel out when multiplied together:

(8\text{ mA}) \times (4.5\text{ k}\Omega) = 8 \times 4.5\text{ V} = 36\text{ V}

.

Estimated Time:1m 0s

Question 122Question →

In basic electronics, distinguishing between charge behavior, measurement units, and current flow conventions is essential. Match each electrical concept on the left with its correct definition or governing rule on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Electron Flow Theory matches the movement of negative charge carriers from negative to positive; Conventional Current Theory matches the historical assumption of flow from positive to negative; Electric Current matches the rate of charge flow over time; One Ampere matches one coulomb of charge per second.

Each electrical term accurately maps to its standard scientific definition: Electron Flow describes negative electrons drifting toward the positive terminal; Conventional Current describes the standard positive-to-negative circuit model; Electric Current represents the rate of charge flow (

I = Q/t

); and One Ampere specifically equals one coulomb passing a given point in one second (

1\text{ C/s}

).

Step-by-Step Solution

1

Identify the physical reality of electron drift versus historical convention.

Electrons are negatively charged, so they drift from negative to positive (Electron Flow). Conventional current historically assumes flow from positive to negative.

Clear differentiation between historical convention and physical subatomic movement is foundational in electrical fundamentals.

2

Define the quantity of electric current.

Current (

I

) represents the rate of charge (

Q

) flow per unit time (

t

), yielding

I = \frac{Q}{t}

.

Current measures the flow rate of charge through a conductor, not electrical pressure or potential difference.

3

Relate the ampere to fundamental SI electrical units.

1\text{ ampere} = 1\text{ coulomb per second}

(

1\text{ A} = 1\text{ C/s}

).

The ampere quantifies current flow as a unit of coulombs transferred over time in seconds.

Key Concept

Fundamental definitions of electric current, charge rate, ampere units, and directional flow models.

Alternative Method

Recall the fundamental dimensional relationships: Current is

I = \frac{\Delta Q}{\Delta t}

, so its unit (

1\text{ A}

) must be equal to

\frac{1\text{ C}}{1\text{ s}}

. Then remember that because electrons possess a negative charge, like charges repel and opposite charges attract, forcing them to move away from the negative terminal toward the positive terminal.

Estimated Time:45s

Question 123Question →

In electrical and electronic systems, understanding the fundamental physical properties governing current flow is essential. Match each resistance-related concept on the left with its correct physical description on the right.

Click a left item, then click its matching right item

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Answer

Electrical Resistance matches the total opposition of a specific component in ohms; Material Resistivity matches the intrinsic geometry-independent material property; American Wire Gauge matches the inverse sizing scale where smaller numbers mean thicker wire; and Positive Temperature Coefficient matches the increase in resistance as temperature rises.

Each electrical concept matches its core definition: Electrical Resistance (

R

) is the total opposition to current flow in ohms; Material Resistivity (

\rho

) is the intrinsic material property; American Wire Gauge (AWG) is the inverse sizing standard where smaller numbers indicate thicker conductors; and a Positive Temperature Coefficient defines the increase of resistance with rising temperature.

Step-by-Step Solution

1

Distinguish between total electrical resistance and intrinsic material resistivity.

Electrical resistance (

R

) is the overall opposition in a specific conductor measured in ohms (

\Omega

), while resistivity (

\rho

) is the inherent property of the material itself.

Total resistance depends on both the material's resistivity and its physical dimensions according to

R = \rho \frac{L}{A}

.

2

Analyze standard conductor sizing and thermal behavior principles.

AWG numbers inversely scale with conductor diameter (smaller number = thicker wire), and a positive temperature coefficient means resistance rises with heat.

Wire gauge dictates cross-sectional area, and thermal excitation in metals increases electron collisions, raising resistance.

Key Concept

Core physical factors and definitions governing electrical resistance and resistivity in conductors

Estimated Time:45s

Question 124Question →

In direct-current (DC) circuit analysis, different forms of Watt's Law are used depending on which electrical quantities are known. Match each set of known circuit parameters on the left with the correct formula on the right used to calculate the target value directly.

Click a left item, then click its matching right item

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Answer

Each given set of circuit parameters matches the direct algebraic form of Watt's Law designed for those specific variables: Voltage and Current to

P = V \times I

; Current and Resistance to

P = I^2 \times R

; Voltage and Resistance to

P = \frac{V^2}{R}

; and Power and Voltage to

I = \frac{P}{V}

.

Each match correctly pairs the given known variables with the exact Watt's Law equation variant required to solve directly for the unknown quantity without needing extraneous calculation steps.

Step-by-Step Solution

1

Identify the base definition of electrical power in terms of voltage and current.

P = V \times I

Power in watts equals electromotive force in volts multiplied by electron current flow in amperes.

2

Derive the power formula when only current and resistance are given using Ohm's Law (

V = I \times R

).

P = (I \times R) \times I = I^2 \times R

Replacing voltage with the product of current and resistance calculates power without needing voltage explicitly.

3

Derive the power formula when only voltage and resistance are given using Ohm's Law (

I = \frac{V}{R}

).

P = V \times \left(\frac{V}{R}\right) = \frac{V^2}{R}

Replacing current with voltage divided by resistance calculates power without needing current explicitly.

4

Rearrange the primary power formula to solve for current when power and voltage are known.

I = \frac{P}{V}

Dividing both sides of

P = V \times I

by voltage isolates the current parameter.

Key Concept

Watt's Law and its derived variations relate electrical power (

P

), voltage (

V

), current (

I

), and resistance (

R

).

Estimated Time:45s

Question 125Question →

An avionics technician tests a direct current (DC) relay control circuit connected to a $36\text{ V}$ power supply. An in-line ammeter indicates that the relay coil draws a steady current of $75\text{ mA}$ . What is the total electrical resistance of the relay coil?

0.48\text{ }\Omega

480\text{ }\Omega

2.7\text{ }\Omega

2,700\text{ }\Omega

Show answer & explanation

Answer: $480\text{ }\Omega$

Answer

The total electrical resistance of the relay coil is

480\text{ }\Omega

.

According to Ohm's Law, resistance is determined by dividing voltage by current (

R = \frac{V}{I}

). First, converting the current from milliamperes to amperes gives

75\text{ mA} = 0.075\text{ A}

. Dividing the

36\text{ V}

supply by

0.075\text{ A}

yields a resistance of

480\text{ }\Omega

.

Step-by-Step Solution

1

Convert the measured current from milliamperes to base amperes.

I = 75\text{ mA} = 75 \times 10^{-3}\text{ A} = 0.075\text{ A}

Standard electrical calculations using Ohm's law require values to be expressed in base SI units (volts, amperes, and ohms).

2

Apply Ohm's law rearranged to solve for resistance (

R = \frac{V}{I}

).

R = \frac{36\text{ V}}{0.075\text{ A}} = 480\text{ }\Omega

Resistance equals electromotive force (voltage) divided by current flow.

Key Concept

Calculating resistance in a DC circuit using Ohm's Law with metric prefix conversion.

Estimated Time:1m 0s

Question 126Question →

A technician connects a 12-volt direct-current (DC) power supply to a two-way radio circuit. According to electron flow theory, how do charge carriers physically move through the external wiring?

Electrons move from the positive terminal, through the radio, toward the negative terminal.

Electrons move from the negative terminal, through the radio, toward the positive terminal.

Electrons oscillate back and forth in place without any net directional movement through the circuit.

Electromotive force creates static potential across the wire without causing physical particle drift.

Show answer & explanation

Answer: Electrons move from the negative terminal, through the radio, toward the positive terminal.

Answer

Electrons move from the negative terminal, through the radio, toward the positive terminal.

In solid metallic conductors, electric current is the physical drift of free electrons. Because electrons have a negative charge, they are repelled by the negative terminal of the DC power source and attracted toward the positive terminal through the external circuit.

Step-by-Step Solution

1

Identify the nature of the power source and charge carriers

The circuit is powered by a direct-current (DC) source where charge carriers in metallic conductors are negatively charged electrons.

Understanding the carrier polarity is essential for determining movement under an electric field.

2

Apply electrostatic attraction and repulsion principles

Electrons carry a negative charge and are therefore repelled by the negative battery terminal and attracted toward the positive terminal.

Like charges repel and opposite charges attract.

3

Determine the physical direction in the external path

In the external circuit outside the power supply, electron flow proceeds from the negative terminal through the load to the positive terminal.

Electron flow theory describes the actual physical movement of electrons.

Key Concept

Electron flow theory dictates that in a DC circuit, electrons drift through the external conductor from the negative terminal to the positive terminal.

Estimated Time:35s

Question 127Question →

An electromagnet is constructed by winding insulated copper wire around a soft iron core. Which of the following modifications will increase the strength of the magnetic field generated by this electromagnet?

Reversing the direction of current flow through the coil

Increasing the electric current flowing through the coil

Replacing the iron core with a non-magnetic plastic core

Maintaining a high voltage across an open circuit in the coil

Show answer & explanation

Answer: Increasing the electric current flowing through the coil

Answer

Increasing the electric current flowing through the coil

The magnetic field strength of an electromagnet depends directly on the magnitude of the electric current flowing through the windings, the number of wire turns, and the permeability of the core material. Increasing the current directly increases the magnetic flux density.

Step-by-Step Solution

1

Identify the factors determining the magnetic field strength of an electromagnet

The field strength of a solenoid or electromagnet depends directly on the electric current, the number of coil turns, and the magnetic permeability of the core.

Electromagnetic flux density is directly proportional to ampere-turns (

I \times N

) and core permeability.

2

Evaluate the proposed modification against the operational formula

Raising the current (

I

) increases the total magnetomotive force (

MMF = N \cdot I

), thereby producing a stronger magnetic field.

Greater electron movement generates more concentric magnetic lines of force around each loop of wire.

Key Concept

The strength of an electromagnet's magnetic field is directly proportional to the magnitude of current flowing through its windings.

Estimated Time:45s

Question 128Question →

Which of the following factors causes an increase in the electrical resistance of a solid metallic wire?

Increasing the cross-sectional area of the wire

Decreasing the overall length of the wire

Increasing the operating temperature of the wire

Using a wire material with higher electrical conductivity

Show answer & explanation

Answer: Increasing the operating temperature of the wire

Answer

Increasing the operating temperature of the wire causes an increase in its electrical resistance.

In metallic conductors, electrical resistance increases as temperature rises. The added thermal energy causes the atoms in the metal lattice to vibrate more vigorously, resulting in more frequent collisions with moving free electrons and hindering the flow of electric current.

Step-by-Step Solution

1

Identify the relationship between temperature and electrical resistance in metallic conductors.

Standard metals have a positive temperature coefficient of resistance, meaning resistance rises as temperature increases.

Thermal energy causes atoms in the metal lattice to vibrate more intensely, increasing collisions with flowing electrons.

2

Evaluate the effects of wire geometry and material properties using the resistance formula.

Electrical resistance is given by

R = \rho \frac{L}{A}

. Resistance increases with greater length (

L

) and higher resistivity (

\rho

), but decreases with larger cross-sectional area (

A

) or higher conductivity.

Analyzing all choices confirms that among the options provided, only increasing the temperature results in higher resistance.

Key Concept

Physical factors governing conductor resistance (temperature coefficient, geometry, and material resistivity)

Estimated Time:45s

Question 129Question →

A technician is servicing an off-grid solar telemetry station and measures the operating parameters of four distinct direct current (DC) load circuits. Match each circuit description on the left with its corresponding calculated electrical quantity on the right using Ohm's law.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The

24\text{ V}

fan at

120\text{ }\Omega

matches

0.20\text{ A}

; the

48\text{ V}

beacon at

16\text{ mA}

matches

3.0\text{ k}\Omega

; the

15\text{ V}

heater drawing

2.5\text{ A}

matches

6.0\text{ }\Omega

; and the

50\text{ mA}

indicator across

180\text{ }\Omega

matches

9.0\text{ V}

.

Each match correctly applies the appropriate algebraic variation of Ohm's law (

V = I \times R

,

I = \frac{V}{R}

, or

R = \frac{V}{I}

) while properly converting metric units (

1\text{ mA} = 0.001\text{ A}

and

1\text{ k}\Omega = 1000\text{ }\Omega

).

Step-by-Step Solution

1

Calculate the current for the cooling fan circuit

I = \frac{V}{R} = \frac{24\text{ V}}{120\text{ }\Omega} = 0.20\text{ A}

Ohm's law defines current as voltage divided by resistance.

2

Calculate the resistance for the remote sensor beacon

R = \frac{V}{I} = \frac{48\text{ V}}{0.016\text{ A}} = 3000\text{ }\Omega = 3.0\text{ k}\Omega

Convert milliamperes to amperes (

16\text{ mA} = 0.016\text{ A}

) and solve for resistance by dividing voltage by current.

3

Calculate the resistance for the environmental heating strip

R = \frac{V}{I} = \frac{15\text{ V}}{2.5\text{ A}} = 6.0\text{ }\Omega

Ohm's law defines resistance as voltage divided by current.

4

Calculate the voltage for the backup LED indicator branch

V = I \times R = 0.050\text{ A} \times 180\text{ }\Omega = 9.0\text{ V}

Convert milliamperes to amperes (

50\text{ mA} = 0.050\text{ A}

) and calculate voltage by multiplying current by resistance.

Key Concept

Ohm's Law states the fundamental relationship between voltage, current, and resistance in a direct current circuit:

V = I \times R

,

I = \frac{V}{R}

, and

R = \frac{V}{I}

.

Estimated Time:1m 15s

Question 130Question →

Electromagnetism and induction are core principles governing how electric circuits interact with magnetic fields. Match each electromagnetic concept with its correct definition or operational description.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Electromagnet matches the temporary magnet created by electric current through a coil; Electromagnetic induction matches the generation of voltage from a changing magnetic field; Mutual induction matches voltage induced in a nearby coil by varying current; Magnetic field lines match imaginary loops representing flux direction and strength.

Each electromagnetic term is matched to its precise definition: an electromagnet creates a magnetic field from electric current; electromagnetic induction creates voltage from a changing magnetic field; mutual induction describes two inductively coupled coils; and magnetic field lines visually represent flux patterns.

Step-by-Step Solution

1

Identify the basic construction and function of an electromagnet.

An electromagnet requires electric current flowing through a coil wound on a ferromagnetic core to produce magnetism.

This pairs 'Electromagnet' directly with the definition describing a temporary magnet formed by current through a wire coil around a core.

2

Define the fundamental principle of electromagnetic induction.

Discovered by Faraday, moving a conductor through a magnetic field or exposing it to changing flux creates an induced voltage.

This matches 'Electromagnetic induction' with the generation of voltage across a conductor experiencing changing magnetic flux.

3

Distinguish mutual induction from general induction.

Mutual induction specifically requires interaction between two distinct coils (primary and secondary).

This links 'Mutual induction' to the definition involving a varying current in one coil inducing voltage across a separate nearby coil.

4

Identify the visual concept used for magnetic flux.

Field lines illustrate lines of magnetic force and field intensity.

This pairs 'Magnetic field lines' with the representation of flux strength and direction.

Key Concept

Core terminology and physical principles of electromagnetism and induction in basic electrical systems.

Estimated Time:45s

Question 131Question →

An electrical circuit that transfers $180\text{ coulombs}$ of charge through a conductor over a span of $3\text{ minutes}$ maintains an electric current of $60\text{ amperes}$ .

True

False

Show answer & explanation

Answer: False

Answer

False. The actual current is

1\text{ A}

because time must be expressed in seconds (

3\text{ minutes} = 180\text{ seconds}

) when calculating current in amperes (

I = \frac{Q}{t}

).

The statement is false because the ampere represents charge transfer per second (

1\text{ A} = 1\text{ C/s}

). A charge of

180\text{ coulombs}

flowing over

3\text{ minutes}

(

180\text{ seconds}

) yields an electric current of exactly

1\text{ ampere}

, not

60\text{ amperes}

.

Step-by-Step Solution

1

Convert the elapsed time from minutes to seconds

3\text{ minutes} \times 60\text{ seconds/minute} = 180\text{ seconds}

The base unit of electric current (ampere) is defined as coulombs per second (

1\text{ A} = 1\text{ C/s}

).

2

Calculate the electric current using the charge rate formula

I = \frac{Q}{t}

I = \frac{180\text{ C}}{180\text{ s}} = 1\text{ A}

Electric current is the rate of charge flow through a cross-section of a conductor.

3

Compare the calculated value with the statement's value

The calculated current is

1\text{ A}

, whereas the statement asserts

60\text{ A}

.

The statement erroneously divides charge by time in minutes rather than seconds.

Key Concept

Electric current is defined as the rate of charge flow per unit time, where one ampere equals one coulomb per second (

I = \frac{Q}{t}

).

Estimated Time:45s

Question 132Question →

A continuous spool of aluminum hookup wire has a total length of $80\text{ meters}$ and a measured electrical resistance of $2.4\ \Omega$ . If an electronics technician cuts a $20\text{-meter}$ piece from this spool for a project, what is the electrical resistance of the cut piece in ohms ( $\Omega$ )?

Show answer & explanation

Answer: 0.6

Answer

0.6 Ω

The electrical resistance of a uniform wire is directly proportional to its length (

R = \rho \frac{L}{A}

). Since

20\text{ m}

is one-fourth (

\frac{1}{4}

or

0.25

) of the original

80\text{ m}

length, the resistance of the cut piece is one-fourth of the total resistance:

2.4\ \Omega \times 0.25 = 0.6\ \Omega

.

Step-by-Step Solution

1

Identify the physical relationship governing wire resistance and length.

Resistance is directly proportional to length:

R = \rho \frac{L}{A}

, which means

R_2 = R_1 \times \frac{L_2}{L_1}

.

Because the material (resistivity

\rho

) and cross-sectional area (

A

) remain constant, resistance scales directly with length.

2

Find the proportion of the new length relative to the original length.

\frac{L_{\text{cut}}}{L_{\text{total}}} = \frac{20\text{ m}}{80\text{ m}} = 0.25

This establishes what fraction of the total opposition to electron flow the shorter segment represents.

3

Calculate the resistance of the 20-meter wire segment.

R_{\text{cut}} = 2.4\ \Omega \times 0.25 = 0.6\ \Omega

Multiplying the total resistance by the length ratio yields the exact resistance of the cut section.

Key Concept

The electrical resistance of a conductor is directly proportional to its length (

R \propto L

) when cross-sectional area and material remain constant.

Estimated Time:45s

Question 133Question →

An HVAC technician is testing a motorized zone damper actuator powered by a $24\text{ V}$ direct current (DC) power supply. An ammeter connected in series measures a current draw of $400\text{ mA}$ through the actuator coil. What is the electrical resistance of the actuator coil?

0.06\text{ }\Omega

9.6\text{ }\Omega

60\text{ }\Omega

9.6\text{ k}\Omega

Show answer & explanation

Answer: $60\text{ }\Omega$

Answer

The electrical resistance of the damper actuator coil is

60\text{ }\Omega

.

According to Ohm's Law, resistance is calculated by dividing the voltage across the component by the current flowing through it (

R = \frac{V}{I}

). Converting

400\text{ mA}

to amperes yields

0.4\text{ A}

. Dividing

24\text{ V}

by

0.4\text{ A}

gives

60\text{ }\Omega

.

Step-by-Step Solution

1

Convert the measured current from milliamperes (mA) to base amperes (A)

I = 400\text{ mA} = \frac{400}{1000}\text{ A} = 0.4\text{ A}

Standard electrical calculations using Ohm's Law require current to be expressed in amperes.

2

State and apply the Ohm's Law formula solved for resistance (

R

)

R = \frac{V}{I}

Resistance equals electromotive force (voltage) divided by current.

3

Substitute the known values and calculate the resistance

R = \frac{24\text{ V}}{0.4\text{ A}} = 60\text{ }\Omega

Dividing

24

by

0.4

gives the coil resistance in ohms.

Key Concept

Ohm's Law (

R = \frac{V}{I}

) and metric prefix conversion

Estimated Time:1m 0s

Question 134Question →

A technician is testing a direct current (DC) cooling fan motor installed in an equipment rack. When powered by a $48\text{ V}$ DC supply, the motor draws a steady current of $250\text{ mA}$ . What is the electrical resistance of the cooling fan motor in ohms ( $\Omega$ )?

Show answer & explanation

Answer: 192

Answer

The electrical resistance of the cooling fan motor is

192\text{ }\Omega

.

According to Ohm's law, resistance is found by dividing voltage by current (

R = \frac{V}{I}

). Converting

250\text{ mA}

to

0.25\text{ A}

and dividing

48\text{ V}

by

0.25\text{ A}

gives exactly

192\text{ }\Omega

.

Step-by-Step Solution

1

Convert the current from milliamperes to amperes

I = 250\text{ mA} = 0.25\text{ A}

Ohm's law calculations require current to be expressed in the base SI unit of amperes.

2

Calculate resistance using Ohm's law formula (

R = \frac{V}{I}

)

R = \frac{48\text{ V}}{0.25\text{ A}} = 192\text{ }\Omega

Dividing the supply voltage by the total circuit current yields the resistance in ohms.

Key Concept

Calculating resistance using Ohm's law (

R = \frac{V}{I}

) combined with metric prefix conversion from milliamperes to amperes.

Estimated Time:1m 0s

Question 135Question →

According to the principles of electromagnetic induction, what occurs in a closed wire loop when the surrounding magnetic field changes?

The electrical resistance of the wire drops completely to zero.

A voltage is generated only while the magnetic field remains completely stationary.

An electric current is induced to flow through the wire.

The wire is permanently converted into an electrical insulator.

Show answer & explanation

Answer: An electric current is induced to flow through the wire.

Answer

An electric current is induced to flow through the wire.

Electromagnetic induction occurs when a changing magnetic field cuts across a conductor, creating an electromotive force (voltage). In a closed loop, this induced voltage causes an electric current to flow.

Step-by-Step Solution

1

Identify the relationship between changing magnetic fields and conductors

A changing magnetic field cutting across a conductor generates an electromotive force (EMF).

Faraday's Law of Induction establishes that voltage is generated whenever magnetic flux lines cross a conductive path.

2

Apply the generated electromotive force to a closed circuit

The induced EMF causes electric current to circulate through the complete loop.

In any closed conductive loop, an induced potential difference creates electron flow.

Key Concept

Electromagnetic induction (generation of voltage and current via changing magnetic flux)

Estimated Time:40s

Question 136Question →

A continuous direct-current (DC) power feed delivers a steady current of $5\text{ amperes}$ through a heavy-duty copper busbar. Which statement correctly describes the physical flow of charge representing this $5\text{ A}$ current?

An electromotive force of five volts is continuously exerted across the length of the busbar.

Five coulombs of electric charge pass through a cross-section of the busbar each second.

Five coulombs of positive charge carriers travel from the negative terminal toward the positive terminal every minute.

Five alternating oscillations of charge direction occur back and forth along the busbar each second.

Show answer & explanation

Answer: Five coulombs of electric charge pass through a cross-section of the busbar each second.

Answer

Five coulombs of electric charge pass through a cross-section of the busbar each second.

Electric current (

I

) measures the rate at which charge passes through a conductor. One ampere (

1\text{ A}

) is defined as one coulomb (

1\text{ C}

) of electrical charge passing through a cross-sectional area in one second (

1\text{ s}

). Therefore, a steady current of

5\text{ A}

means that

5\text{ coulombs}

of charge pass through the cross-section of the busbar every second.

Step-by-Step Solution

1

Identify the fundamental definition of electric current and its standard unit.

Current (

I

) is defined as the rate of transfer of electric charge (

Q

) per unit of time (

t

), expressed by the formula

I = \frac{Q}{t}

.

The ampere is the base SI unit of electrical current, defined as one coulomb of charge passing a point per second (

1\text{ A} = 1\text{ C/s}

).

2

Apply the given current value of

5\text{ A}

to the rate formula.

I = 5\text{ A} = \frac{5\text{ coulombs}}{1\text{ second}}

.

A steady current of

5\text{ A}

directly translates to a charge flow rate of

5\text{ coulombs per second}

through the conductor.

Key Concept

Electric current is the time rate of charge flow through a conductor, where one ampere equals one coulomb per second (

I = Q/t

).

Estimated Time:40s

Question 137Question →

A magnetic field is generated around a conductor only when alternating current (AC) flows through it, whereas direct current (DC) produces no magnetic field.

True

False

Show answer & explanation

Answer: False

Answer

False

The statement is false because any flow of electric current through a conductor creates a magnetic field. Direct current (DC) produces a steady, non-fluctuating magnetic field around the wire, while alternating current (AC) produces an expanding and collapsing magnetic field.

Step-by-Step Solution

1

Identify the fundamental relationship between electric current and magnetic fields.

Electric current is the movement of electric charge, and any moving charge produces a magnetic field around its path.

This is the core principle of electromagnetism discovered by Hans Christian Oersted.

2

Evaluate the behavior of direct current (DC) in a conductor.

A steady direct current produces a steady, stationary magnetic field forming concentric circular lines of flux around the conductor.

A constant current still consists of moving electrical charges, which continuously maintain a magnetic field.

3

Distinguish between magnetic field generation and electromagnetic induction.

While electromagnetic induction (generating a voltage in another conductor) requires a changing magnetic field (such as from AC), generating a magnetic field itself requires only the presence of electric current.

Confusing field generation with transformer induction leads to the false belief that DC cannot produce magnetism.

Key Concept

Magnetic Field Generation by Electric Current

Estimated Time:35s

Question 138Question →

In direct-current (DC) circuits, understanding the fundamental definitions, units, and directional models of electric charge is essential for troubleshooting. Match each electrical current concept on the left with its correct physical description or definition on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Electron Flow Theory pairs with the physical drift of negative charge carriers from negative to positive; Conventional Current Theory pairs with the classical convention of positive charge moving from positive to negative; Electric Current Rate (

1\text{ A}

) pairs with one coulomb passing per second; and Total Electric Charge (

1\text{ C}

) pairs with the quantity of charge from

6.24 \times 10^{18}

electrons.

Each concept accurately reflects its physical and scientific definition: electron flow describes negative carriers moving negative-to-positive, conventional flow describes positive-to-negative modeling, an ampere defines charge rate per second, and a coulomb defines total accumulated electron charge.

Step-by-Step Solution

1

Differentiate between the two current flow directional models

Electron flow represents actual negative charge carriers moving from negative to positive terminals, while conventional flow designates positive charge moving from positive to negative terminals.

Clear separation of physical electron movement from historical circuit conventions prevents directional polarity errors.

2

Distinguish rate of flow (current) from static quantity of charge

Current measured in amperes (

1\text{ A} = 1\text{ C/s}

) represents the rate of charge transfer, whereas charge measured in coulombs (

1\text{ C} \approx 6.24 \times 10^{18}\text{ electrons}

) represents the accumulated charge quantity.

Differentiating rate (

I = Q/t

) from total charge (

Q

) is fundamental to quantitative circuit analysis.

3

Verify all four concept-to-definition pairings

Each electrical concept on the left uniquely and unambiguously aligns with its physical definition on the right.

Ensures complete matching accuracy without conceptual overlap.

Key Concept

Electric current is the time rate of charge flow through a conductor (

I = Q/t

), where electrons physically drift from negative to positive potentials while conventional current is modeled from positive to negative.

Estimated Time:45s

Question 139Question →

An electronics technician is sorting materials for a repair job based on their electrical properties. Arrange the following materials in order from the highest electrical conductivity (best conductor) to the lowest electrical conductivity (best insulator).

Drag items to arrange them in the correct order

Show answer & explanation

Answer

Copper, Germanium, Rubber

Metals like copper have a high concentration of free electrons, making them excellent conductors. Group IV elements such as germanium act as semiconductors with intermediate conductivity. Non-metallic compounds like rubber hold their electrons tightly in covalent structures, acting as insulators with the lowest conductivity.

Step-by-Step Solution

1

Identify the conductor among the materials

Copper is identified as a conductor with high electrical conductivity.

Conductors have loosely bound valence electrons that move freely under an applied voltage.

2

Identify the semiconductor among the materials

Germanium is identified as a semiconductor with moderate electrical conductivity.

Semiconductors have four valence electrons and exhibit conductivity between conductors and insulators.

3

Identify the insulator among the materials

Rubber is identified as an insulator with extremely low electrical conductivity.

Insulators hold valence electrons tightly, offering very high resistance to current flow.

4

Sequence the materials from highest to lowest electrical conductivity

Copper (conductor)

\rightarrow

Germanium (semiconductor)

\rightarrow

Rubber (insulator)

The ranking follows the natural continuum of charge carrier availability in solids.

Key Concept

Classification and relative electrical conductivity of conductors, semiconductors, and insulators.

Estimated Time:45s

Question 140Question →

An automated assembly fixture uses an industrial direct current (DC) solenoid valve to actuate a pneumatic clamp. The solenoid coil has an internal resistance of $600\text{ }\Omega$ and requires a steady current of $35\text{ mA}$ to operate reliably. What DC voltage must the power supply deliver to the solenoid valve?

17.1\text{ V}

2.1\text{ V}

21\text{ V}

21,000\text{ V}

Show answer & explanation

Answer: $21\text{ V}$

Answer

21\text{ V}

According to Ohm's Law, voltage is calculated by multiplying current by resistance (

V = I \times R

). Converting the current from milliamperes to amperes gives

35\text{ mA} = 0.035\text{ A}

. Multiplying

0.035\text{ A} \times 600\text{ }\Omega

results in

21\text{ V}

.

Step-by-Step Solution

1

Convert the operating current from milliamperes (

\text{mA}

) to base amperes (

\text{A}

).

35\text{ mA} = \frac{35}{1,000}\text{ A} = 0.035\text{ A}

Ohm's Law calculations require electrical quantities in standard SI base units.

2

Apply Ohm's Law (

V = I \times R

) to find the required supply voltage.

V = 0.035\text{ A} \times 600\text{ }\Omega = 21\text{ V}

Voltage equals the product of current and resistance.

Key Concept

Ohm's Law (

V = I \times R

) with metric prefix conversion

Estimated Time:1m 0s

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