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Fiber practice questions

46 questions from the low voltage and structured cabling practice test.

Fiber practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

What jacket colour identifies indoor OM3 or OM4 laser-optimised multimode cable?

  1. Orange
  2. Aqua
  3. Yellow
  4. Lime green
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B. Aqua

OM3 and OM4 are jacketed aqua. Orange is used for the older OM1 and OM2 multimode, yellow for single-mode and lime green for OM5 wideband multimode.

Reference: ANSI/TIA-598, fibre colour coding

Which pair of wavelengths is normally used to test and operate single-mode fibre?

  1. 1310 nm and 1550 nm
  2. 850 nm and 1300 nm
  3. 650 nm and 850 nm
  4. 850 nm and 1550 nm
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A. 1310 nm and 1550 nm

Single-mode systems operate and are tested at 1310 and 1550 nm. 850 and 1300 nm are the multimode windows, and 650 nm is visible red light used by fault locators.

Reference: ANSI/TIA-568.3; TIA-526-7

Light stays in the core of an optical fibre by total internal reflection. What property of the glass makes that possible?

  1. The cladding has a higher refractive index than the core
  2. The core has a higher refractive index than the cladding
  3. The cladding is coated with a thin reflective metal layer
  4. The core and cladding have exactly the same refractive index
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B. The core has a higher refractive index than the cladding

Light striking the boundary from a higher-index core to a lower-index cladding at a shallow enough angle is reflected back completely. If the cladding had the higher index, light would refract out of the core and be lost.

Reference: Fibre optic theory; FOA reference guide

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