IB Physics SL C.3.4 Total Internal Reflection

Practise checking both conditions for total internal reflection, calculating critical angle from refractive indices and tracing rays in prisms, fibres or layered media.

Exam points

confirm light travels from higher to lower refractive index before testing the incidence angle
calculate sinθc = n₂/n₁ and compare the actual incidence angle with the critical angle
trace total reflection or refraction at each boundary in a prism or fibre without assuming every interface reflects

[Maximum number: 2]

Monochromatic light enters the base of a plastic beaker that contains water with an oil layer floating on it. A student draws a diagram to show the directions the light takes as it passes through the layers. The student's diagram has one error at position A and one error at position B. The refractive indices of the materials are shown on the diagram.

Figure for Question C.3.4—Total internal reflection question 1 — IB Physics SL

The light is refracted at an angle of $32^{\circ}$ when it enters the plastic layer as shown.

Calculate the critical angle for the plastic-water interface.

$\begin{aligned} \frac{\sin i}{\sin r}=\frac{1.33}{1.60} \text { and } \sin r=1 i=\lessdot \sin ^{-1} 0.831 »=56<^{\circ} \gg \end{aligned}$

Accept 0.98 rad (unit required)

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C.3.4—Total internal reflection question 1