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Critical angle and total internal reflection

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Overview

Recall questions on the critical angle, its relationship to refractive index, total internal reflection and the conditions for it, and investigating it with a semi-circular block.

What you need to know

Answer each one before you reveal it.

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Key term

What is varied during an investigation of total internal reflection using a semi-circular block?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is varied during an investigation of total internal reflection using a semi-circular block?

    Model answer

    The angle of incidence at the flat face.

  2. 2

    What phenomena can be observed at the flat face of a semi-circular block as the angle of incidence is increased?

    Model answer

    Refraction and total internal reflection.

  3. 3

    Define the critical angle.

    Model answer

    The angle of incidence in the denser medium at which the angle of refraction in the less dense medium is exactly 90°.

  4. 4

    State the equation relating the critical angle to the refractive index.

    Model answer

    sin C = 1/n, where C is the critical angle and n is the refractive index of the denser medium relative to the less dense medium.

  5. 5

    Write the formula used to calculate the critical angle from the refractive index.

    Model answer

    C = arcsin(1/n).

  6. 6

    Define total internal reflection.

    Model answer

    Total internal reflection occurs when light travelling in a denser medium strikes the boundary with a less dense medium at an angle greater than the critical angle.

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