N10-009 Network Implementation Practice Question
A company has just installed a new fiber optic connection between two buildings 2 km apart. The connection is using multimode fiber. However, the signal is too weak at the receiving end. What is the most likely cause?
⚠ Common exam trap
CompTIA often tests the misconception that fiber is immune to all distance limitations, but the trap here is that multimode fiber has strict distance limits due to modal dispersion and higher attenuation, unlike single-mode fiber which can span 2 km easily.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Attenuation due to distance
Multimode fiber (MMF) is designed for shorter distances, typically up to 550 meters for 10 Gbps (OM3/OM4) and up to 2 km only for lower speeds like 100 Mbps or 1 Gbps using older OM1/OM2 fiber. At 2 km, the signal attenuation exceeds the power budget of the MMF link, causing a weak signal at the receiver. Single-mode fiber (SMF) would be required for reliable transmission over this distance.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Attenuation due to distance
Why this is correct
Multimode fiber, commonly used for shorter distances within buildings, experiences significant signal loss, known as attenuation, over extended runs. Its larger core allows for multiple light paths, leading to modal dispersion which limits effective transmission distance, especially at higher data rates. A 2 km link far exceeds the typical maximum reach for multimode fiber, which is often less than 550 meters for 10 Gigabit Ethernet, resulting in substantial signal degradation. This distance limitation directly causes the observed signal weakening.
- ✗
Electromagnetic interference
Why it's wrong here
Fiber optic cables transmit data as pulses of light through a glass or plastic core, making them fundamentally immune to electromagnetic interference (EMI). Unlike copper cabling, which relies on electrical signals susceptible to external electromagnetic fields from power lines, motors, or radio frequencies, fiber optics are unaffected. Therefore, EMI cannot induce signal weakening or data corruption in a fiber optic connection, rendering it an irrelevant factor for this issue.
- ✗
Incorrect termination
Why it's wrong here
While incorrect termination can cause light loss, the most likely issue over such a long distance is distance-related attenuation. Termination issues are more likely to cause total failure or high loss at the connection points, not gradual weakening along the run.
When this WOULD be correct
A question where a fiber link shows high loss but the distance is within spec (e.g., 100 meters), and the connectors are visibly dirty or poorly polished. In that case, incorrect termination (e.g., bad splice or dirty connector) is the likely cause.
- ✗
Crosstalk
Why it's wrong here
Crosstalk is a phenomenon primarily associated with copper cabling, where electromagnetic coupling between adjacent wire pairs causes unwanted signal interference from one circuit to another. Since fiber optic cables transmit data using light pulses within individual glass strands, there is no electromagnetic field generated that could induce interference into an adjacent fiber. Consequently, fiber optic connections are inherently immune to crosstalk, making it an impossible cause for signal weakening in this scenario.
When this WOULD be correct
In a scenario where multiple copper cables (e.g., Cat6a) are run in close proximity for long distances and signal degradation or errors occur on one pair due to interference from another pair, crosstalk would be the correct answer. For example, a question about 1000BASE-T running over 100 meters with high error rates due to adjacent cable interference.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓Attenuation due to distanceCorrect answer▾
Why this is correct
Multimode fiber, commonly used for shorter distances within buildings, experiences significant signal loss, known as attenuation, over extended runs. Its larger core allows for multiple light paths, leading to modal dispersion which limits effective transmission distance, especially at higher data rates. A 2 km link far exceeds the typical maximum reach for multimode fiber, which is often less than 550 meters for 10 Gigabit Ethernet, resulting in substantial signal degradation. This distance limitation directly causes the observed signal weakening.
✗Incorrect terminationWrong answer — click to see why▾
Why this is wrong here
Incorrect termination can cause signal loss, but the question states the fiber is multimode and the distance is 2 km. Multimode fiber is typically limited to about 550 meters at 10 Gbps; the primary issue is attenuation due to exceeding the distance limit, not termination.
★ When this WOULD be the correct answer
A question where a fiber link shows high loss but the distance is within spec (e.g., 100 meters), and the connectors are visibly dirty or poorly polished. In that case, incorrect termination (e.g., bad splice or dirty connector) is the likely cause.
Why candidates choose this
Candidates may confuse general fiber issues like termination problems with distance-related attenuation, especially if they recall that improper termination can cause signal loss, but they overlook the specific distance limitation of multimode fiber.
✗CrosstalkWrong answer — click to see why▾
Why this is wrong here
Crosstalk occurs when signals from adjacent cables interfere with each other, typically in copper cabling (e.g., UTP). Fiber optic cables use light, not electricity, so crosstalk is not a concern, especially over a 2 km multimode link where distance-related attenuation is the primary issue.
★ When this WOULD be the correct answer
In a scenario where multiple copper cables (e.g., Cat6a) are run in close proximity for long distances and signal degradation or errors occur on one pair due to interference from another pair, crosstalk would be the correct answer. For example, a question about 1000BASE-T running over 100 meters with high error rates due to adjacent cable interference.
Why candidates choose this
Candidates may confuse crosstalk with general signal interference or assume that any signal loss in a cable could be caused by interference from nearby cables, not realizing that fiber optics are immune to electromagnetic crosstalk.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
Related to this question
Learn chapter
Link Aggregation: LACP and PAgP
Key term
Receiver
A receiver is a hardware device or software component that accepts incoming signals, data, or transmissions from a sender over a communication channel.
Key term
Multimode fiber
A type of optical fiber that carries multiple light signals simultaneously over short to medium distances, commonly used in local area networks and data centers.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.