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Refraction at a plane surface

  • 5 things to know
  • Papers 1 and 3

Overview

Refractive index and Snell's law, total internal reflection, and optical fibres and dispersion.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Numbers

How is refractive index defined, and what can Snell's law be used to find?

Process

How does the cladding compare with the core, and how does a fibre carry light?

Key term

What is a step index fibre, why is cladding needed, and why does material dispersion occur?

Process

How does pulse broadening affect data transmission in optical fibres?

Key term

Why are repeaters or amplifiers needed along long optical fibre links?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How is the refractive index of a substance defined?

    Model answer

    The refractive index is the ratio of the speed of light in a vacuum to the speed of light in that substance.

  2. 2

    State the formula for refractive index and define each term.

    Model answer

    n = c/cₛ, where n is the refractive index, c is the speed of light in a vacuum, and cₛ is the speed of light in the substance.

  3. 3

    What is the approximate refractive index of air?

    Model answer

    Approximately 1.

  4. 4

    State Snell's law of refraction.

    Model answer

    When light passes from one medium to another, the product of the refractive index and the sine of the angle to the normal remains constant across the boundary.

  5. 5

    Write the equation for Snell's law and identify each symbol.

    Model answer

    n₁ sin θ₁ = n₂ sin θ₂, where n₁ and n₂ are the refractive indices of the first and second media, and θ₁ and θ₂ are the angles of incidence and refraction measured from the normal.

  6. 6

    When applying Snell's law at a boundary, what quantities can be determined if the others are known?

    Model answer

    Unknown angles of incidence or refraction, or unknown refractive indices of either medium.

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