Multimeter: Resistance and Continuity Practice Questions — Armed Services Vocational Aptitude Battery (ASVAB)

Question 1Question →

A technician is using a digital multimeter to test a standard cartridge fuse that has been removed from a circuit. If the fuse is intact and in good working condition, what reading should the multimeter display when set to measure resistance?

Infinite resistance or

\text{OL}

(Over Limit)

Approximately

0\ \Omega

(zero or near-zero resistance)

A voltage reading matching the circuit source voltage

A very high resistance in the megaohm (

\text{M}\Omega

) range

Show answer & explanation

Answer: Approximately $0\ \Omega$ (zero or near-zero resistance)

Answer

Approximately

0\ \Omega

(zero or near-zero resistance)

A functional, intact fuse is a continuous electrical conductor designed to offer almost zero opposition to current flow. When tested with a multimeter set to resistance (

\Omega

) or continuity, it will display a reading of approximately

0\ \Omega

, confirming complete circuit continuity.

Step-by-Step Solution

1

Identify the internal state of a good fuse.

An unbroken conductive metallic link inside the fuse casing.

Fuses are protective conductors designed to allow electrical current to pass with negligible opposition during normal operation.

2

Determine the expected ohmmeter reading across a continuous conductor.

The meter reads zero or near-zero ohms (

0\ \Omega

).

An ohmmeter sends a tiny test current through the component; because the path is unbroken and non-resistive, resistance is measured at virtually

0\ \Omega

.

Key Concept

Multimeter resistance and continuity testing across closed conductors versus open circuits

Estimated Time:45s

Question 2Question →

When troubleshooting electrical circuits with a digital multimeter set to measure resistance ( $\Omega$ ), the display reading reflects the physical state of the circuit path. Match each digital multimeter display reading with its corresponding circuit condition.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Zero ohms (

0.0\ \Omega

) matches a continuous, closed path; over-limit (

\text{OL}

) matches an open circuit or broken conductor; and a finite numerical value (

150\ \Omega

) matches a functional resistive load.

A reading of

0.0\ \Omega

indicates that the path is continuous with zero opposition to current. An over-limit display (

\text{OL}

) indicates infinite resistance, which occurs when a conductor is broken or a switch is open. A finite numerical value such as

150\ \Omega

represents an intact resistive component operating normally.

Step-by-Step Solution

1

Interpret the zero resistance reading (

0.0\ \Omega

)

Identified as full continuity

When meter leads are connected across a continuous conductor or closed switch, opposition to current is zero.

2

Interpret the infinite reading (

\text{OL}

)

Identified as an open circuit

An interrupted path or broken filament does not permit electron flow, resulting in infinite resistance beyond the meter range.

3

Interpret the finite numeric reading (

150\ \Omega

)

Identified as a normal resistive component

Operational electrical components such as heating elements or resistors have a rated non-zero resistance value.

Key Concept

Interpreting Digital Multimeter Resistance and Continuity Display Readings

Estimated Time:45s

Question 3Question →

What critical safety precaution must always be taken before using a digital multimeter to measure the resistance of a component in an electrical circuit?

Keep the circuit energized so the ohmmeter can utilize the system's operating current

Ensure all electrical power to the circuit is completely disconnected and de-energized

Insert the black test lead into the high-amperage terminal port instead of the common port

Wrap the component terminals with electrical insulating tape before applying the test probes

Show answer & explanation

Answer: Ensure all electrical power to the circuit is completely disconnected and de-energized

Answer

Ensure all electrical power to the circuit is completely disconnected and de-energized

A multimeter's ohmmeter or continuity function operates by applying a small internal voltage from its own battery across the component leads and measuring the resulting current flow. If external power is present, the external voltage interferes with the measurement circuitry, causes invalid readings, and risks blowing internal protective fuses or damaging the instrument. Therefore, disconnecting and verifying zero power is the primary safety rule.

Step-by-Step Solution

1

Identify the operating principle of a multimeter set to measure resistance (

\Omega

)

The meter outputs its own low internal DC voltage from an internal battery to pass a known test current through the component and calculate resistance via Ohm's Law (

R = \frac{V}{I}

).

Understanding how the meter measures resistance clarifies why external circuit power disrupts the measurement.

2

Determine the necessary condition of the circuit under test

The circuit must have zero external voltage and zero external current flow.

Any live voltage present on the test leads will alter the calculation, blow the meter's internal fuse, or pose an electrical hazard.

Key Concept

Multimeter Ohmmeter Safety and De-energization Requirement

Estimated Time:45s

Question 4Question →

An electronic technician needs to measure the resistance of a resistor installed on a circuit board to verify its value. What is the correct sequence of steps to safely and accurately perform this measurement?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

Disconnect power to the circuit

\rightarrow

Isolate at least one lead of the resistor

\rightarrow

Set the multimeter dial to resistance (

\Omega

)

\rightarrow

Place the test probes across the component leads and observe the display.

The correct sequence begins with de-energizing the circuit for safety and instrument protection, isolating at least one lead to eliminate parallel circuit paths, configuring the multimeter to the Ohms function, and finally contacting the leads across the component to observe the reading.

Step-by-Step Solution

1

Ensure all power to the circuit is disconnected.

The circuit is completely de-energized and safe to work on.

Multimeters measure resistance by supplying their own small internal voltage; external power will damage the meter and produce invalid readings.

2

Lift or disconnect at least one lead of the resistor from the circuit board.

The resistor is isolated from other components.

Parallel paths in the circuit network would provide alternative current loops, causing the meter to read lower than the true component value.

3

Turn the rotary switch on the multimeter to the resistance (

\Omega

) range.

The multimeter is configured in ohmmeter mode.

The meter must be in the correct mode before probes are applied to the device under test.

4

Connect the black and red test leads across the resistor terminals.

The resistance value appears on the digital readout.

The meter sends a small internal current through the component, measures the resulting voltage drop, and displays the calculated resistance.

Key Concept

Safely and accurately measuring component resistance requires de-energizing the circuit, isolating the component from parallel paths, selecting the Ohms mode, and applying the test probes.

Estimated Time:45s

Question 5Question →

When diagnosing electrical circuits with a digital multimeter (DMM) set to measure resistance ( $\Omega$ ) or continuity, different display readings indicate specific circuit and component conditions. Match each multimeter reading to its corresponding electrical condition:

Click a left item, then click its matching right item

Show answer & explanation

Answer

The closed switch reading of

0.0\ \Omega

with a beep matches a continuous unbroken path; the

\text{OL}

reading on a

24\ \Omega

element matches an internal open circuit; the

4.7\ \text{k}\Omega

reading matches normal component resistance; and fluctuating readings with a voltage warning match measuring resistance on an energized circuit.

Each pair directly aligns the meter display with fundamental circuit states:

0.0\ \Omega

with a beep indicates unbroken continuity;

\text{OL}

on a load component signifies an open-circuit failure; a reading matching component ratings indicates proper health; and erratic values with a voltage warning indicate power was improperly left connected.

Step-by-Step Solution

1

Evaluate the zero-ohm reading with an audible tone

Identifies full continuity (closed path)

Multimeters use continuity mode to verify a continuous electrical path; zero ohms represents negligible resistance across closed switch contacts.

2

Evaluate the infinite resistance (OL) reading on a load component

Identifies an open circuit condition

A healthy

24\ \Omega

heating element should read approximately

24\ \Omega

; an OL reading indicates the internal filament or element wire is completely severed.

3

Evaluate the

4.7\ \text{k}\Omega

reading against the resistor color bands

Identifies normal nominal operation

Yellow (

4

), violet (

7

), and red multiplier (

10^2 = 100

) equals

4700\ \Omega

or

4.7\ \text{k}\Omega

, matching the measured reading.

4

Evaluate erratic values accompanied by a meter voltage warning

Identifies a live-circuit testing safety violation

Resistance must always be measured on fully de-energized circuits. Live current backfeeding into the meter distorts the internal test current and triggers warnings.

Key Concept

Interpreting digital multimeter resistance and continuity readings under open, closed, nominal, and live-circuit conditions

Estimated Time:1m 15s

Question 6Question →

An apprentice technician connects digital multimeter test leads across an unpowered, unbroken length of copper wire to verify circuit continuity. Which multimeter response confirms that the wire provides a continuous, unbroken electrical path?

An overload or open-loop reading (

\text{OL}

) with no tone

A continuous audible tone accompanied by a resistance reading near

0\ \Omega

A very high resistance reading in the megaohm (

\text{M}\Omega

) range

A fluctuating DC voltage reading measured in millivolts (

\text{mV}

)

Show answer & explanation

Answer: A continuous audible tone accompanied by a resistance reading near $0\ \Omega$

Answer

A continuous audible tone accompanied by a resistance reading near

0\ \Omega

When a digital multimeter is set to continuity mode, it sends a tiny test current through the leads. When placed across an unbroken conductor, the resistance is nearly

0\ \Omega

, which closes the test loop and activates the meter's audible beeper.

Step-by-Step Solution

1

Identify the purpose of a continuity check

A continuity test verifies whether an unbroken path exists for electrical current to flow.

Continuity requires a low-resistance physical connection between two test points.

2

Determine the expected resistance and meter behavior for a good conductor

An intact copper conductor exhibits minimal resistance (close to

0\ \Omega

), which causes the multimeter's internal continuity buzzer to sound continuously.

Digital multimeters sound a continuous audible beep when the measured resistance across the leads is below a designated threshold (typically under

30\ \Omega

to

50\ \Omega

).

Key Concept

Multimeter continuity mode detects complete electrical paths by measuring near-zero resistance and emitting an audible tone.

Estimated Time:45s

Question 7Question →

While troubleshooting a de-energized printed circuit board, a technician measures the resistance across a $10\text{ k}\Omega$ resistor that remains fully soldered in place. The digital multimeter displays a steady reading of $2.4\text{ k}\Omega$ . What is the primary cause of this lower resistance reading?

The circuit must be energized so that the multimeter internal sensing circuit receives sufficient operating voltage.

The test current from the multimeter is flowing through alternate parallel paths connected across the circuit board.

The resistor has experienced an internal breakdown and formed a complete electrical short circuit.

The multimeter leads were placed across the component in reverse polarity without zeroing the test leads.

Show answer & explanation

Answer: The test current from the multimeter is flowing through alternate parallel paths connected across the circuit board.

Answer

The test current from the multimeter is flowing through alternate parallel paths connected across the circuit board.

A digital multimeter measures resistance by injecting a small internal test voltage and measuring the resulting current. When measuring a component that is still soldered into a circuit, that test current splits across the component and any other interconnected parallel branches. Because parallel resistance combinations always result in an equivalent resistance smaller than the smallest branch (

R_{total} < R_{branch}

), the meter registers a lower value (

2.4\text{ k}\Omega

) than the resistor's nominal rating (

10\text{ k}\Omega

). To obtain an accurate reading, at least one lead of the component must be disconnected or desoldered.

Step-by-Step Solution

1

Analyze the measurement environment and the component's circuit state.

The resistor is measured while fully connected (in-circuit) to other components on the board.

Components soldered onto a circuit board are rarely isolated and typically connect to adjacent traces, semiconductors, or resistors.

2

Apply parallel circuit principles to the ohmmeter test current.

The ohmmeter supplies a small internal test current across the probes, which divides among all available conductive paths between those two nodes.

According to the laws of parallel resistance, adding parallel paths always reduces the total equivalent resistance below the value of the lowest single branch (

R_{eq} < R_1

).

3

Determine the necessary troubleshooting procedure for an accurate reading.

Isolate at least one terminal/lead of the resistor from the circuit board before measuring.

Desoldering one leg breaks parallel loop paths, ensuring 100% of the meter's test current flows strictly through the component under test.

Key Concept

In-circuit resistance measurement, component isolation, and parallel path loading

Estimated Time:1m 0s

Question 8Question →

A technician needs to test a household appliance heating element for continuity and resistance using a digital multimeter. What is the correct chronological sequence of steps to perform this measurement safely and accurately?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct chronological sequence is: first disconnect the appliance power supply, second disconnect at least one wire lead to isolate the heating element, third insert the test leads and set the multimeter dial to resistance, fourth touch probe tips together to verify meter zeroing and lead continuity, and fifth place the probe tips across the heating element terminals to read the resistance value.

The correct sequence follows standard electronics testing protocol: power must always be disconnected first for safety, the component must be isolated to prevent parallel loop paths from skewing readings, the meter must be properly set up, test leads must be shorted to verify zero calibration, and finally the probes are applied to measure the isolated component.

Step-by-Step Solution

1

Disconnect electrical power from the appliance.

The appliance is completely de-energized.

Multimeters use an internal battery to pass a known current for resistance measurement; external voltage can blow the meter fuse, destroy internal circuitry, or cause electric shock.

2

Detach at least one wire connection from the heating element.

The component is electrically isolated from surrounding circuitry.

Leaving both ends connected allows current to pass through parallel components, resulting in a false, lower resistance reading.

3

Plug black lead into COM, red lead into

\Omega

, and select the resistance range on the meter dial.

The digital multimeter is configured for resistance mode.

Proper jack selection and mode switching ensure the meter applies its internal reference voltage and measures current correctly.

4

Touch the test probe tips together.

The display indicates close to

0\ \Omega

.

This confirms good test lead integrity, proper meter zero reference, and active battery power.

5

Contact the probe tips to the two heating element terminals.

The true component resistance is displayed.

The meter measures the voltage drop across the isolated resistance element to calculate and display its value.

Key Concept

Safe and accurate multimeter resistance and continuity measurements require complete circuit de-energization, component isolation, proper lead/meter configuration, calibration verification, and direct terminal contact.

Estimated Time:1m 15s

Question 9Question →

An automotive technician tests an unpowered single-pole single-throw (SPST) toggle switch that has been removed from a vehicle's dashboard. With the digital multimeter set to the resistance ( $\Omega$ ) mode and the switch set to the OFF position, what should the meter display across the switch terminals if the switch is functioning normally?

An infinite resistance or "OL" (overload) reading, indicating an open circuit

A reading of approximately

0\text{ }\Omega

with a continuous beep, indicating a complete path for current

A constant reading of

12\text{ V}

, representing the supply voltage held across the open contacts

A reading of several kilo-ohms (

\text{k}\Omega

) that gradually drops to zero once the circuit is energized

Show answer & explanation

Answer: An infinite resistance or "OL" (overload) reading, indicating an open circuit

Answer

An infinite resistance or "OL" (overload) reading, indicating an open circuit

When an SPST toggle switch is placed in the OFF position, its internal mechanical contacts are physically separated. This creates an open circuit with infinite electrical resistance. A digital multimeter set to resistance (

\Omega

) or continuity mode will display this condition as "OL" (overload / open loop) or infinite resistance (

\infty

), confirming that no current can flow across the open terminals.

Step-by-Step Solution

1

Identify the physical state of the switch contacts in the OFF position

The internal mechanical contacts are physically separated (open)

An SPST switch in the OFF position interrupts the current path by creating an air gap between terminals.

2

Determine how a digital multimeter interprets an open path in resistance (

\Omega

) mode

The meter measures infinite resistance, displayed as "OL" or "

\infty

"

An open circuit provides no path for the multimeter's internal sensing current to return.

Key Concept

Interpreting open circuit resistance readings on a digital multimeter

Estimated Time:1m 0s

Question 10Question →

When using a digital multimeter (DMM) to measure resistance and evaluate circuit continuity, specific testing conditions and technician techniques directly determine the accuracy and validity of the measurement. Match each resistance testing scenario with its direct diagnostic outcome or operational effect.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Measuring on a live circuit injects voltage and risks meter damage; touching both probes during megaohm tests creates a parallel body resistance path that lowers the reading; in-circuit testing without isolating a terminal measures unintended parallel circuit loops; and testing an intact fuse or closed contact displays near

0\ \Omega

with an audible beep.

Each testing scenario matches its fundamental electrical principle: live circuits overload the internal ohmmeter; bare skin contact places body resistance in parallel to artificially lower high-value measurements; in-circuit testing introduces parallel circuit paths; and an unbroken fuse provides zero resistance and triggers the continuity tone.

Step-by-Step Solution

1

Evaluate the safety and operational constraints of multimeter ohmmeter circuits

Identified that ohmmeter circuits must never be connected to live sources, matching live-circuit measurement to meter damage and false voltage injection.

Ohmmeters inject internal reference voltage; external energized voltage opposes or overloads the measurement circuit.

2

Analyze the impact of unintended parallel paths from human body contact and board circuitry

Matched finger contact to body parallel resistance error, and in-circuit component measurement to alternate component loops reducing equivalent resistance.

According to parallel circuit rules, any additional parallel resistive branch reduces the total equivalent resistance (

R_{\text{eq}} < R_{\text{branch}}

).

3

Determine the response of an intact conductor under continuity mode

Matched isolated intact fuse or closed contact to near

0\ \Omega

reading and continuous tone.

Continuity mode detects complete low-resistance loops typically below

30\text{--}50\ \Omega

and indicates them with an audible buzzer.

Key Concept

Multimeter resistance measurements require de-energized circuits, proper probe handling, component isolation to prevent parallel loading, and recognition that

0\ \Omega

indicates continuity whereas high or open paths do not beep.

Estimated Time:1m 15s

Question 11Question →

An avionics technician is inspecting a de-energized multi-conductor wiring harness to verify that no internal short circuits exist between adjacent wires. With both ends of the harness completely disconnected from all components and power sources, the technician sets a digital multimeter to the resistance ( $\Omega$ ) function and connects the test leads across two separate, insulated conductors. If the insulation between these two conductors is completely intact, what should the multimeter display?

A reading of approximately

0\ \Omega

, confirming continuity between the two conductors.

An over-limit or infinite resistance reading (

OL

), indicating an open circuit between the conductors.

A fluctuating DC voltage reading generated by the meter's internal measurement circuit.

A nominal resistance of approximately

10\ \Omega

, reflecting standard conductor insulation resistance.

Show answer & explanation

Answer: An over-limit or infinite resistance reading ( $OL$ ), indicating an open circuit between the conductors.

Answer

An over-limit or infinite resistance reading (

OL

), indicating an open circuit between the conductors.

When testing between two separate, properly insulated wires in a de-energized harness, there should be no conductive path between them. A digital multimeter set to resistance mode will measure this absence of continuity as infinite resistance, displayed on the digital screen as 'OL' (open loop/over-limit).

Step-by-Step Solution

1

Analyze the circuit state and component relationship under test.

Two distinct conductors in a disconnected wiring harness are separated by insulation and should have no electrical connection between them.

Intact insulation ensures complete electrical isolation between separate conductors.

2

Determine the expected electrical resistance between two isolated conductors.

Because no conductive path exists, the resistance between the conductors is theoretically infinite (an open circuit).

An open circuit allows zero current flow between isolated paths.

3

Identify how a digital multimeter indicates infinite resistance in resistance measurement mode.

Digital multimeters display 'OL' (over-limit/open loop) or infinity to indicate an open circuit exceeding the meter's range.

The meter detects no closed loop or measurable current between its test leads.

Key Concept

Multimeter interpretation of open circuits vs. shorts during insulation and continuity testing

Estimated Time:1m 0s

Question 12Question →

An avionics technician is troubleshooting a de-energized, three-conductor wiring harness that is disconnected at both ends. Using a digital multimeter set to the resistance ( $\Omega$ ) mode, the technician records the following measurements:

- Probing between Conductor 1 and Conductor 2 at the near end yields a reading of $0.3\ \Omega$ .
- Probing between Conductor 1 and Conductor 3 at the near end yields a reading of $\text{OL}$ (overload/infinite resistance).
- After placing a temporary jumper wire between Conductor 1 and Conductor 3 at the far end, probing between Conductor 1 and Conductor 3 at the near end continues to read $\text{OL}$ .

Which of the following diagnoses is conclusively supported by these test results?

Conductor 1 and Conductor 2 have an open circuit, while Conductor 3 maintains normal end-to-end continuity.

Conductor 1 and Conductor 2 are shorted together, and Conductor 3 has an internal open circuit fault.

All conductors are intact, but accurate resistance and continuity readings require the harness to be connected to live operating voltage.

Conductor 1 and Conductor 2 demonstrate normal dielectric insulation, whereas the

\text{OL}

reading indicates zero resistance.

Show answer & explanation

Answer: Conductor 1 and Conductor 2 are shorted together, and Conductor 3 has an internal open circuit fault.

Answer

Conductor 1 and Conductor 2 are shorted together, and Conductor 3 has an internal open circuit fault.

In a de-energized, disconnected harness, isolated conductors should show infinite resistance (

\text{OL}

). The

0.3\ \Omega

reading between Conductor 1 and Conductor 2 indicates an unintended low-resistance connection (short circuit). When a jumper is placed at the far end between Conductor 1 and Conductor 3, a closed loop should be formed with near-zero resistance; the persistent

\text{OL}

display proves the path is broken, confirming an open circuit fault in Conductor 3.

Step-by-Step Solution

1

Analyze the resistance measurement between disconnected Conductors 1 and 2.

A reading of

0.3\ \Omega

between two wires that should be electrically isolated indicates continuity where none should exist.

Independent conductors in a disconnected harness should exhibit infinite resistance (open circuit). A reading near

0\ \Omega

confirms an insulation breakdown or physical short circuit between Conductors 1 and 2.

2

Evaluate the loop continuity test between Conductors 1 and 3 with a far-end jumper installed.

The multimeter continues to read

\text{OL}

(overload / infinite resistance).

Jumpering two conductors at the far end forms a continuous loop. If both conductors and the jumper were intact, the near-end resistance should be near zero. A reading of

\text{OL}

indicates that the loop is broken, identifying an open circuit in Conductor 3 (since Conductor 1 is continuous as established in the first test).

3

Synthesize the two findings into a definitive circuit diagnosis.

Conductors 1 and 2 are shorted together, and Conductor 3 is open.

Both fault conditions are independently verified by standard multimeter resistance and continuity interpretation rules.

Key Concept

Interpreting Multimeter Resistance and Continuity Readings in Wiring Fault Diagnosis

Question 13Question →

An industrial technician is troubleshooting an unpowered control cabinet and needs to measure the electrical resistance of a 24-volt relay coil to determine if the internal winding is defective. What is the correct chronological sequence of steps the technician should follow to perform this measurement safely and accurately?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The technician must first verify the circuit is de-energized, disconnect at least one coil terminal to isolate it from parallel paths, configure the multimeter into resistance mode with correct lead placement, apply the test probes across the coil terminals, and finally compare the resulting reading against manufacturer specifications.

The correct procedural order begins with personal and equipment safety by de-energizing the circuit, followed by component isolation to eliminate parallel resistance paths. Next, the multimeter is properly configured with leads in COM and V/

\Omega

ports on the resistance setting. The probes are then placed across the terminals to obtain a reading, and the sequence finishes by comparing the measured value to the manufacturer's technical specifications.

Step-by-Step Solution

1

Ensure all power to the system is shut down and locked out.

The control circuit is fully de-energized and safe for ohmmeter connection.

Ohmmeter circuits inject their own small reference current; measuring on a live circuit will blow meter fuses or cause severe damage.

2

Disconnect at least one conductor from the relay coil terminals.

The relay coil is electrically isolated from any parallel components.

Parallel circuit paths provide alternative routes for test current, resulting in false, lower-than-actual resistance readings.

3

Connect the black lead to COM, red lead to V/

\Omega

, and turn the dial to the

\Omega

range.

The meter is correctly set up to inject reference current and compute resistance from voltage drop.

Placing leads in current (A/mA) jacks or selecting incorrect functions causes measurement failure or errors.

4

Apply probe tips firmly to the two coil terminals and wait for a stable reading.

The multimeter displays the true resistance of the coil winding.

Firm probe pressure minimizes contact resistance and ensures accurate measurement.

5

Evaluate the measured resistance relative to published technical data.

Accurate diagnostic determination of whether the coil is operational, shorted (near

0\ \Omega

), or open (OL).

A reading matching nominal specifications indicates a good coil, while significant deviations indicate faults.

Key Concept

Multimeter resistance testing requires a strictly ordered procedure: de-energizing power for safety, isolating the component to eliminate parallel paths, configuring proper meter settings, taking the measurement, and comparing results with specifications.

Estimated Time:1m 0s

Question 14Question →

A technician is using a digital multimeter (DMM) set to the resistance ( $\Omega$ ) and continuity modes to troubleshoot de-energized components on an industrial electrical bench. Match each multimeter measurement reading on the left with its corresponding diagnostic circuit condition on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The normally open switch reading 'O.L' matches the normal open-circuit state for separated contacts; the AC line-to-chassis reading of

0.1\,\Omega

matches the severe line-to-ground short circuit fault; the motor coil reading 'O.L' matches the burned-out internal open winding failure; and the indicator lamp reading

18\,\Omega

matches the normal continuous conductive path for an intact resistive load.

Each multimeter reading directly correlates to the internal electrical state of the component: an open contact set produces infinite resistance ('O.L'), an unintended low-resistance connection between hot conductors and frame ground represents a dead short (

0.1\,\Omega

), a severed coil wire destroys continuity ('O.L'), and a continuous resistive filament yields its nominal cold resistance (

18\,\Omega

).

Step-by-Step Solution

1

Evaluate the normally open (NO) switch measurement

Display reads 'O.L' (

> 40\text{ M}\Omega

)

When de-actuated, NO switch contacts are physically separated by air (an insulator), so infinite resistance is the expected normal condition.

2

Evaluate the AC line terminal to chassis ground measurement

Display reads

0.1\,\Omega

Power conductors should be electrically isolated from structural metal enclosures. A near-zero reading indicates a dangerous short circuit / ground fault.

3

Evaluate the motor stator winding measurement against its nominal

3.5\,\Omega

rating

Display reads 'O.L' with no continuity beep

Because the coil should form a continuous low-resistance inductive path, an over-limit reading proves the wire has melted or fractured into an open circuit.

4

Evaluate the incandescent lamp filament measurement

Display reads

18\,\Omega

An intact metal filament has low finite resistance at ambient temperature, confirming circuit continuity and normal component health.

Key Concept

Interpreting digital multimeter resistance and continuity display values (zero ohms, nominal ohms, over-limit / O.L) to distinguish between normal component states, open-circuit faults, and short circuits.

Estimated Time:1m 30s

Question 15Question →

A technician is using a digital multimeter set to the resistance ( $Ω$ ) function to test a de-energized DC solenoid valve coil with a nominal rating of $24\ \Omega$ . Which multimeter display reading indicates that the solenoid coil has an internal open circuit?

0.0\ \Omega

24\ \Omega

\text{OL}

(over-limit) or infinite resistance

24\ \text{k}\Omega

Show answer & explanation

Answer: $\text{OL}$ (over-limit) or infinite resistance

Answer

An over-limit (OL) or infinite resistance reading on the digital multimeter display indicates an open circuit.

An open circuit occurs when there is a physical break in the conductive path of the coil winding. Because electric current cannot bridge the gap, the electrical resistance across the terminals becomes infinite (

\infty

). On a digital multimeter, infinite resistance that exceeds the instrument's measurement capability is displayed as 'OL' (over-limit).

Step-by-Step Solution

1

Identify the electrical state being tested on the de-energized coil.

An internal open circuit means the continuous wire winding has broken, creating an incomplete path.

When a conductor or winding breaks, current can no longer pass through the component.

2

Determine the theoretical resistance value of an open circuit.

An open circuit provides infinite resistance (

\infty\ \Omega

) to the multimeter's internal test current.

Air or physical gaps between broken wire ends have extremely high dielectric resistance.

3

Correlate infinite resistance with standard digital multimeter display conventions.

Digital multimeters display infinite resistance exceeding the measurement range as 'OL' (over-limit) or '

\infty

'.

Multimeters use 'OL' to indicate that the measured resistance exceeds the measurable range of the selected scale.

Key Concept

Interpreting digital multimeter resistance displays for open circuits versus normal continuity

Estimated Time:1m 0s

Question 16Question →

An electronics technician is bench-testing a de-energized two-position rotary selector switch using a digital multimeter set to the low-resistance continuity function. With the switch set to Position 1, the meter connected across the common terminal and output terminal 1 displays $0.2\ \Omega$ with an audible tone. When the switch is turned to Position 2, the meter across the common terminal and output terminal 1 continues to display $0.2\ \Omega$ , while testing across the common terminal and output terminal 2 displays $\text{O.L.}$ (over limit). What specific switch fault do these multimeter readings indicate?

The common terminal insulator has broken down into a conductor, creating an open circuit on all switch positions.

The internal contacts for Position 1 are welded or shorted closed, while the contacts for Position 2 have failed open.

The meter is reading residual circuit voltage, which forces the resistance display to read zero ohms regardless of contact position.

The switch is functioning normally because a reading of

\text{O.L.}

indicates zero resistance and continuous current flow.

Show answer & explanation

Answer: The internal contacts for Position 1 are welded or shorted closed, while the contacts for Position 2 have failed open.

Answer

The internal contacts for Position 1 are welded or shorted closed, while the contacts for Position 2 have failed open.

A reading of

0.2\ \Omega

with an audible tone confirms a closed, continuous electrical path. When the rotary switch is moved to Position 2, output terminal 1 should disconnect and display

\text{O.L.}

; because it remains at

0.2\ \Omega

, the Position 1 contacts are welded or shorted closed. Simultaneously, output terminal 2 should establish continuity in Position 2; showing

\text{O.L.}

indicates an open circuit where contacts failed to close.

Step-by-Step Solution

1

Analyze the baseline continuity measurement in Position 1.

A reading of

0.2\ \Omega

with an audible tone indicates a normal, closed, continuous connection between the common terminal and output terminal 1.

Digital multimeters indicate continuity with near-zero resistance and an audible beeper.

2

Evaluate the resistance between common and terminal 1 after switching to Position 2.

The meter continues to read

0.2\ \Omega

, meaning the contacts remained closed instead of opening.

When rotated away from Position 1, the contacts should open and show infinite resistance (

\text{O.L.}

); failing to do so indicates contacts welded or mechanically shorted closed.

3

Evaluate the resistance between common and terminal 2 in Position 2.

The meter displays

\text{O.L.}

, indicating an open circuit.

In Position 2, terminal 2 should connect to common with near-zero ohms; an over-limit reading proves the contacts failed to make contact (open circuit defect).

Key Concept

Interpreting multimeter resistance and continuity values (

0\ \Omega

vs.

\text{O.L.}

) to diagnose internal short-circuit and open-circuit defects in multi-position switches.

Estimated Time:1m 15s

Question 17Question →

An electronics technician is troubleshooting a printed circuit board. The circuit originally consisted of a DC power supply and three resistors: $R_1$ ( $100\ \Omega$ ), $R_2$ ( $150\ \Omega$ ), and $R_3$ ( $300\ \Omega$ ). $R_2$ and $R_3$ are wired in parallel with each other. This parallel pair is connected in series with $R_1$ , and the entire resistor network is connected across the power supply terminals.

To prepare for resistance testing, the technician completely removes the power supply. However, they accidentally leave a solid copper jumper wire connected across the two empty terminals where the power supply was attached.

Without desoldering any components, the technician sets a digital multimeter (DMM) to measure resistance and places the probes directly across the leads of $R_2$ . Assuming all resistors are functioning normally, what resistance reading will the DMM display?

50\ \Omega

100\ \Omega

150\ \Omega

200\ \Omega

Show answer & explanation

Answer: $50\ \Omega$

Answer

The multimeter will display

50\ \Omega

because it measures the equivalent resistance of all parallel paths in the closed loop.

The multimeter measures the equivalent resistance of all parallel paths between its probes. The jumper wire connects

R_1

in parallel with the

R_2

and

R_3

branches. The equivalent resistance of

100\ \Omega

,

150\ \Omega

, and

300\ \Omega

in parallel is

50\ \Omega

.

Step-by-Step Solution

1

Determine the original circuit topology.

R_1

is in series with the parallel pair of

R_2

and

R_3

.

This establishes the baseline connections before the power supply was removed.

2

Analyze the effect of the jumper wire.

The jumper wire connects the open ends of the circuit, creating a closed loop. It connects the free end of

R_1

directly to the common ground/return path of

R_2

and

R_3

.

This fundamentally changes the topology, placing

R_1

in parallel with

R_2

and

R_3

from the perspective of the components.

3

Identify what the DMM measures when placed across

R_2

.

The DMM measures the total equivalent resistance between the two nodes of

R_2

.

A multimeter cannot isolate a component in a closed circuit; it reads all active parallel paths.

4

Calculate the equivalent resistance of the three parallel branches (

R_1

,

R_2

,

R_3

).

1/R_{eq} = 1/100 + 1/150 + 1/300 = 3/300 + 2/300 + 1/300 = 6/300

.

R_{eq} = 300 / 6 = 50\ \Omega

.

To find the final reading displayed by the meter.

Key Concept

In-Circuit Resistance Measurement and Component Isolation

Question 18Question →

An electronics technician is troubleshooting a complex, completely de-energized control panel. Match each component testing scenario using a digital multimeter (DMM) to its expected meter reading and diagnostic meaning.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Intact wire matches to 0.0 ohms and a beep; the in-circuit 10k resistor matches to 2k ohms due to parallel paths; the isolated relay coil matches to a specific nominal resistance; and the blown fuse matches to OL (infinite resistance).

Each scenario accurately reflects standard DMM behavior. Intact wires show continuity (0 ohms/beep). Components measured in-circuit show parallel equivalent resistance (

2\ \text{k}\Omega

for a 10k and 2.5k parallel combination). Relay coils have measurable nominal resistance, and blown fuses read as open circuits (OL).

Step-by-Step Solution

1

Analyze the intact copper wire scenario.

Matches to 'Displays 0.0 ohms and emits a continuous beep'.

A solid wire has negligible resistance, representing a perfect short or closed circuit.

2

Evaluate the in-circuit resistor measurement.

Matches to 'Displays approximately 2 kOhms'.

The DMM measures the total equivalent resistance of the parallel circuit path. Using the formula

R_{eq} = \frac{R_1 \times R_2}{R_1 + R_2}

, the result is

\frac{10 \times 2.5}{10 + 2.5} = 2\ \text{k}\Omega

.

3

Determine the reading for an isolated, functional relay coil.

Matches to 'Displays a specific, steady nominal resistance'.

Relay coils are made of thin wire wound many times, which inherently possesses a measurable nominal resistance (unlike a dead short).

4

Identify the reading for a blown fuse.

Matches to 'Displays OL or 1.'.

A blown fuse breaks the circuit path, resulting in infinite resistance (an open circuit).

Key Concept

Digital Multimeter Resistance and Continuity Interpretation

Multimeter: Resistance and Continuity

Answer

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