Self-Study Package for Total Internal Reflection

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Instructions• Download and print out the document “Supplementary WS

TIR.doc”• You should go through these slides and work on the

worksheets concurrently. Hence it is suggested that you do your worksheet in front of your computer and run this presentation.

• You should complete each section in the worksheet, check your answer to each section (in this presentation) BEFORE moving on to the next section.

• E.g. do section 2.1 first on the worksheet, check the answer to section 2.1 in this presentation, then move on to do section 2.2 on the worksheet.

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Answers• Click on the buttons below for the answer to each section• DO NOT see the answer before you attempt the question

yourself first!

1.1

3.2

3.6

4.3

2.1

3.3

3.7

4.4

2.2

3.4

4.1

4.5

3.1

3.5

4.2

4.6

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4.1

4.5 4.6

Section 1.1

• Angle of Incidence (i) = Angle of Reflection (ii)

Section 2.1

• Light bends away from the normal, when it is going from more dense to less dense.

Section 2.2

• This equation is only valid if light is going from medium to air

Section 3.1 (Fig 3.1)• n = sin r / sin i• (1.5) = sin r / sin (35.5)• sin r = (1.5)[(sin (35.5)] = 0.8711 (note: 4 sig. fig.)• r = sin-1 (0.8711)• = 60.59° (note: 2 d.p.)• = 60.6° (final answer: 1 d.p.)

60.6°

Section 3.1 (Fig 3.2)• n = sin r / sin i• (1.5) = sin r / sin (38.8)• sin r = (1.5)[(sin (38.8)] = 0.9399• r = sin-1 (0.9399)• = 70.03°• = 70.0° (1 d.p.)

70.0°

Section 3.1 (Fig 3.3)• n = sin r / sin i• (1.5) = sin r / sin (41.0)• sin r = (1.5)[(sin (41.0)] = 0.9841 (4 sig. fig)• r = sin-1 (0.9841)• = 79.77°• = 79.8° (1 d.p.)

79.8°

Section 3.2

• The refracted ray is getting closer and closer to the horizontal edge of the block• The angle of refraction r is approaching 90°

Section 3.3• We want to find i, when r = 90°• Recall, n = 1.5• n = sin r / sin i• (1.5) = sin 90 / sin i• sin i = (sin 90) / (1.5) = 0.6667• i = sin-1(0.6667)• = 41.81°• = 41.8° (1 d.p.)

90°

48.1°

Section 3.4

• Critical Angle

Section 3.5• refer to textbook page 231 (Pure Physics), or 189 (Science

Physics)• The angle of incidence in an optically denser medium for

which the angle of refraction in the optically less dense medium is 90°

• [Please memorize]

Section 3.6• EITHER OR

Section 3.7• For water (n = 1.33)• sin c = 1/n• = 1/(1.33) = 0.7519• c = sin-1 (0.7519) • = 48.8°

• For diamond (n = 2.41)• sin c = 1/n• = 1/(2.41) = 0.4149• c = sin-1 (0.4149)• = 24.5°

Section 4.1

• Total internal reflection occurs• Demo: http://

www.youtube.com/watch?v=8VZHym6HqVU

Section 4.2

• [refer to pg 231 (Pure Physics), or pg 189 (Science Physics)]• The complete reflection of a light ray inside an optically

denser medium at its boundary with an optically less dense medium.• [please memorize]

Section 4.3• i = 45°• c = 41.8°• i > c, therefore total internal reflection occurs

45°45°

Section 4.4

• For both cases, reflection occurs, and i = r• Note: n = sin i/sin r does NOT apply

Section 4.5

• 1) Light ray going from more dense to less dense medium• 2) Angle of incidence is greater than critical angle• [please memorize this]

Section 4.6 (Case A)• sin c = 1/n• sin c = 1/(1.34) = 0.7463• c = sin-1 (0.7463) = 48.3°• i < c, hence total internal reflection

does not occur. Light goes through and is refracted.

• n = sin r/sin i• 1.34 = sin r/sin 45• sin r = (1.34)(sin 45) = 0.9475• r = sin-1(0.9475)• r = 71.4°

71.4°

Section 4.6 (Case B)• sin c = 1/n• sin c = 1/(1.83) = 0.5464• c = sin-1 (0.5464) = 33.1°• i > c, hence total internal reflection occurs• i = r

35°35°

Section 4.6 (Case C)• from section 3.3, c = 41.8°• i > c, but total internal reflection does

NOT occur, as light is going from less dense to more dense medium.

• Light passes through and is refracted• n = sin i/ sin r• (1.5) = sin 45/sin r• sin r = sin 45/(1.5) = 0.4714• r = sin-1(0.4714) = 28.1°

28.1°

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