IB Physics HL C 3 4 Total Internal Reflection Questions

Practise IB Physics HL C.3.4 by solving critical-angle and fibre-acceptance problems and tracing rays across multiple optical boundaries.

Exam points

Check the direction of travel and compare the incidence angle with the critical angle to justify TIR.
Calculate the critical angle using the refractive indices on the two sides of the boundary.
Rearrange the critical-angle relation to find a refractive index or the speed of light in a medium.
Use the critical angle, boundary geometry and Snell’s law to find a fibre’s maximum entrance angle.
Distinguish a ray’s angle to the fibre axis from its incidence angle at the core–cladding boundary.
Sketch the reflected and emerging rays, measuring angles to the normal at each optical boundary.
Predict how changes in refractive index and ray direction can turn a critical ray into a reflected ray.

[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 IB Physics HL C 3 4 Total Internal Reflection Questions question 1 — IB Physics HL

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.

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

Accept 0.98 rad (unit required)

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IB Physics HL C 3 4 Total Internal Reflection Questions question 1