Total Internal Reflection and Critical Angle Insights

1. 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.

2. 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.

3. 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.

4. 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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5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

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

True

False

Partial reflection still happens.

Explanation

Partial reflection still happens.

12. 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.

13. 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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