AQA AS Level Physics Paper 2, June 2024: Question 21

1 mark · Easy difficulty · Multiple Choice

Identify the correct statement regarding the cladding of a step-index optical fibre.

Practise this question

Question

Multiple choice question 21 worth 1 mark, asking about the purpose or property of the cladding of a step-index optical fibre. Four options are given: A, must not be transparent; B, must have a higher refractive index than the core; C, reduces signal loss; D, reduces material dispersion. Each option has a selection box next to it.
Question text

21 The cladding of a step-index optical fibre

[1 mark]

A must not be transparent.

B must have a higher refractive index than the core.

C reduces signal loss.

D reduces material dispersion.

Mark scheme

Show the mark scheme The mark scheme table shows question number 21 with the correct answer C, corresponding to 'reduces signal loss.'

21 C reduces signal loss.

How to answer it

The Purpose of Cladding in a Step-Index Optical Fibre

What this question tests

This question assesses your fundamental knowledge of optical fibre construction, specifically the role and function of the cladding layer in total internal reflection, maintaining signal integrity, and preventing optical interference.

Question 21

Multiple Choice Question (1 Mark)

✅ Correct Answer

C — reduces signal loss.

Awarded 1 mark for selecting C.

💡 Key Knowledge

  • Refractive Index: The cladding must have a lower refractive index than the core to enable total internal reflection at the core-cladding boundary.
  • Signal Protection: Cladding protects the core surface from scratches, dirt, and moisture, which causes light to scatter and reduces signal loss (attenuation).
  • Cross-talk Prevention: It prevents light from leaking out of one fibre and entering an adjacent fibre in a bundle.

🧠 Exam Technique

Eliminate incorrect distractors systematically:

  • A is false: The cladding must be transparent so that light isn't heavily absorbed.
  • B is false: Cladding needs a lower refractive index than the core, not higher.
  • D is false: Material dispersion is minimized by using monochromatic light or narrow core sizes, not primarily by the cladding.

❌ Common Errors

A frequent student mistake is confusing optical fibre components. Many mistakenly believe cladding increases refractive index (option B) or confuses signal degradation with dispersion mechanisms (option D).

Topics

Physics · 3.3 Waves

Question and mark scheme from the AQA AS Level Physics examination, Paper 2, June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.