FE Other Disciplines Practice Question Solution included after investigation
CASE E-099 · FE

The Wire That Had 0.17 Ohm, Not 170

The resistivity formula was correct, but 2 mm² was treated as 2×10^-9 m² instead of 2×10^-6 m². The wire resistance was 0.17 ohm.

▶ INTERACTIVE CASE FILE • 5–10 MIN • CLICK TO INVESTIGATE

Inspect, commit, prove, fix, and sign off.

Case E-099 engineering failure visual
HOW THIS WORKS

Think like
a real engineer.

Follow the investigation process used in the field — in five guided steps.

1

Inspect

Review the problem, diagram, and evidence.

2

Commit

Choose your hypothesis.

3

Prove

Run calculations and test your idea.

4

Fix

Select and validate a safe correction.

5

Sign Off

See the full debrief and key takeaways.

Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

A 20 m conductor has resistivity rho=1.7×10^-8 ohm·m and cross-sectional area 2.0 mm². A note converts the area to 2×10^-9 m² and reports 170 ohm. Determine the correct resistance, voltage drop at 10 A, and conductor power loss.

Materials Other Disciplines Design Verification Root Cause Analysis Safe Correction
E-099
INVESTIGATION WORKSPACE WORK THROUGH THE CASE — YOUR CHOICES MATTER.
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DEBRIEF (LOCKED)

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Find the root cause, confirm the fix, and see how this connects to the exam.

🔒Root causeComplete the case
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🔒Correct fixComplete the case
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🔒Exam takeawayComplete the case
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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

The area unit was converted as a linear dimension.

What was missed

1 mm²=10^-6 m².

Corrected model

Convert area correctly, then use R=rho L/A.

QUICK ANSWER

2 mm²=2×10^-6 m². Therefore R=(1.7×10^-8)(20)/(2×10^-6)=0.17 ohm. At 10 A, voltage drop is 1.7 V and power loss is 17 W.

ENGINEERING TAKEAWAY

Convert squared length units correctly, then use R=rho L/A.

CASE QUESTIONS

Questions this case should settle.

How many square meters is 1 mm²?

1×10^-6 m².

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WHAT YOU’LL LEARN

Real failures. Lasting skills.

Each case is designed to build the judgment, analysis, and confidence you need for engineering exams — and beyond.

  • Apply core engineering concepts to real-world problems
  • Practice structured troubleshooting and analysis
  • Strengthen exam-ready thinking through realistic scenarios
COMMON QUESTIONS
Do I need prior knowledge to use these cases?

Basic subject familiarity helps, but every case is designed to teach through the investigation itself.

How long does a case take?

Most cases are designed for a focused 5–10 minute investigation.

Are the cases aligned with engineering exams?

Each case is mapped to a verified exam, subject, topic, and misconception before publication.

What happens after I complete a case?

The sealed debrief unlocks with the root cause, corrected reasoning, fix, and takeaway.