NOCE Ophthalmic Optics and Formulas 4

Question 1

Using Snell's law, if light strikes glass (n = 1.50) at 30° from the normal in air (n = 1.00), what is the approximate angle of refraction?

Accepted Answer

19.5°

Answer

n₁ sin θ₁ = n₂ sin θ₂ → sin θ₂ = sin 30° / 1.50 = 0.333, so θ₂ ≈ 19.5°.

Question 2

What is the critical angle for total internal reflection in a material with n = 1.50?

Accepted Answer

41.8°

Answer

sin θc = 1/n = 1/1.50 = 0.667; θc = arcsin(0.667) ≈ 41.8°.

Question 3

A lens material with an Abbe value of 30 has more chromatic aberration than a material with an Abbe value of:

Accepted Answer

58

Answer

Higher Abbe values indicate less chromatic dispersion; 58 > 30, so that material has less aberration.

Question 4

The index of refraction of a material is defined as:

Accepted Answer

The ratio of the speed of light in vacuum to the speed of light in the medium

Answer

n = c / v, where c is the speed of light in vacuum and v is the speed in the medium.

Question 5

Standard CR-39 plastic (allyl diglycol carbonate) has an index of refraction of approximately:

Accepted Answer

1.49

Answer

CR-39 has an index of approximately 1.499 (commonly cited as 1.49 or 1.50).

NOCE - National Opticianry Competency Examination Practice Test