Total Internal Reflection and Critical Angle Insights

1. At angles below the critical angle, both refraction and reflection can occur.

True

False

Partial reflection still happens.

Explanation

Partial reflection still happens.

2. Best grade 10 summary: TIR happens when:

Light goes from low n to high n

Light goes from high to low and the angle is above the critical

Light hits the surface at 0°

Light is unpolarized

That’s the required condition.

Explanation

That’s the required condition.

3. A ray in water strikes the surface to air at 60° (critical ~49°). What happens?

Refraction only

Total internal reflection

No reflection

Bends toward the normal

60° > 49° → TIR.

Explanation

60° > 49° → TIR.

4. A ray at exactly the critical angle refracts along the boundary.

True

False

That’s the definition.

Explanation

That’s the definition.

5. If light in glass hits the glass–air boundary at 20° (critical ~42°), the main outcome is:

Total internal reflection

Refraction occurs (plus some reflection)

No transmission

Light becomes polarized automatically

20° < critical angle → refraction happens.

Explanation

20° < critical angle → refraction happens.

6. Total internal reflection (TIR) occurs when light goes:

From low to high n

From high to low at a large incident angle

From air to glass only

From vacuum to air only

TIR needs a higher-to-lower refractive index and incidence above the critical.

Explanation

TIR needs a higher-to-lower refractive index and incidence above the critical.

7. Water to air has n_1 = 1.33, n_2 = 1.00. sin(θ_c) = 1/1.33 ≈ 0.75. θ_c is closest to:

30°

41°

49°

70°

sin(49°) ≈ 0.75.

Explanation

sin(49°) ≈ 0.75.

8. TIR is possible when light goes from water to air.

True

False

n_water > n_air, so a critical angle exists.

Explanation

n_water > n_air, so a critical angle exists.

9. A diamond sparkles strongly partly because it has:

Very low refractive index

High refractive index, giving a small critical angle

No reflection

Zero dispersion

Small critical angle makes TIR more likely inside.

Explanation

Small critical angle makes TIR more likely inside.

10. Optical fibres work because of:

Diffraction

Total internal reflection

Gravitational lensing

Chemical reactions

Light stays trapped by repeated TIR.

Explanation

Light stays trapped by repeated TIR.

11. If the incident angle is greater than θ_c, refraction stops and the light reflects internally.

True

False

That is total internal reflection.

Explanation

That is total internal reflection.

12. Light goes from glass (n=1.50) to air (n=1.00). sin(θ_c) = 1/1.5 ≈ 0.67. θ_c is closest to:

30°

42°

56°

75°

sin(42°) ≈ 0.67.

Explanation

sin(42°) ≈ 0.67.

13. The critical angle is defined only when n_1 > n_2.

True

False

Otherwise sin(θ_c) = n_2/n_1 would be >1 or not meaningful.

Explanation

Otherwise sin(θ_c) = n_2/n_1 would be >1 or not meaningful.

14. If n_1 increases (with n_2 fixed), the critical angle:

Increases

Decreases

Stays the same

Becomes 90°

sin(θ_c) = n_2/n_1; bigger n_1 → smaller ratio → smaller angle.

Explanation

sin(θ_c) = n_2/n_1; bigger n_1 → smaller ratio → smaller angle.

15. Conditions for TIR:

Light in higher-n medium hits boundary to lower-n

Incident angle exceeds critical angle

Light must be red only

No real refracted angle exists (Snell would require sin(θ_2) > 1)

a, b, and d are correct.

Explanation

a, b, and d are correct.

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16. If sin(θ_c) = 0.80, then θ_c is closest to:

37°

45°

53°

65°

sin(53°) ≈ 0.80.

Explanation

sin(53°) ≈ 0.80.

17. TIR violates energy conservation because it reflects all the light.

True

False

Reflection can be total without violating conservation.

Explanation

Reflection can be total without violating conservation.

18. Critical angle satisfies sin(θ_c) = n_2/n_1, where light is going from medium 1 (higher n) to medium 2 (lower n).

The critical angle is defined as the angle of incidence at which light, traveling from a denser medium (with refractive index n_1) to a less dense medium (with refractive index n_2), is refracted at an angle of 90 degrees. At this point, total internal reflection occurs, and the relationship is given by the equation sin(θ_c) = n_2/n_1. This formula indicates that the sine of the critical angle is equal to the ratio of the refractive indices of the two media, emphasizing the dependency on their optical properties.

Explanation

The critical angle is defined as the angle of incidence at which light, traveling from a denser medium (with refractive index n_1) to a less dense medium (with refractive index n_2), is refracted at an angle of 90 degrees. At this point, total internal reflection occurs, and the relationship is given by the equation sin(θ_c) = n_2/n_1. This formula indicates that the sine of the critical angle is equal to the ratio of the refractive indices of the two media, emphasizing the dependency on their optical properties.

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19. At the critical angle, the refracted ray makes an angle of:

0°

30°

60°

90°

It travels along the boundary at 90° to the normal.

Explanation

It travels along the boundary at 90° to the normal.

20. TIR requires n_1 ___ n_2.

Total Internal Reflection (TIR) occurs when light travels from a medium with a higher refractive index (n_1) to a medium with a lower refractive index (n_2). For TIR to happen, the angle of incidence must exceed the critical angle, which is determined by the ratio of the refractive indices. This condition is satisfied only when n_1 is greater than n_2, allowing light to be completely reflected back into the denser medium rather than refracting into the less dense one. Hence, the relationship n_1 > n_2 is essential for TIR.

Explanation

Total Internal Reflection (TIR) occurs when light travels from a medium with a higher refractive index (n_1) to a medium with a lower refractive index (n_2). For TIR to happen, the angle of incidence must exceed the critical angle, which is determined by the ratio of the refractive indices. This condition is satisfied only when n_1 is greater than n_2, allowing light to be completely reflected back into the denser medium rather than refracting into the less dense one. Hence, the relationship n_1 > n_2 is essential for TIR.

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Total Internal Reflection & Critical Angle Quiz

1. At angles below the critical angle, both refraction and reflection can occur.

2.

What first name or nickname would you like us to use?

2. Best grade 10 summary: TIR happens when:

3. A ray in water strikes the surface to air at 60° (critical ~49°). What happens?

4. A ray at exactly the critical angle refracts along the boundary.

5. If light in glass hits the glass–air boundary at 20° (critical ~42°), the main outcome is:

6. Total internal reflection (TIR) occurs when light goes:

7. Water to air has n_1 = 1.33, n_2 = 1.00. sin(θ_c) = 1/1.33 ≈ 0.75. θ_c is closest to:

8. TIR is possible when light goes from water to air.

9. A diamond sparkles strongly partly because it has:

10. Optical fibres work because of:

11. If the incident angle is greater than θ_c, refraction stops and the light reflects internally.

12. Light goes from glass (n=1.50) to air (n=1.00). sin(θ_c) = 1/1.5 ≈ 0.67. θ_c is closest to:

13. The critical angle is defined only when n_1 > n_2.

14. If n_1 increases (with n_2 fixed), the critical angle:

15. Conditions for TIR:

16. If sin(θ_c) = 0.80, then θ_c is closest to:

17. TIR violates energy conservation because it reflects all the light.

18. Critical angle satisfies sin(θ_c) = n_2/n_1, where light is going from medium 1 (higher n) to medium 2 (lower n).

19. At the critical angle, the refracted ray makes an angle of:

20. TIR requires n_1 ___ n_2.