7. Optical Properties of Gems – Refraction of light

Welcome to your Module 7 - Optical Properties of Gems – Refraction of light

1. What is refraction?

Refraction

a) The splitting of light into multiple colors

b) The bending of light as it passes from one medium to another

c) The absorption of light by a material

d) The reflection of light off a surface

2. Which law describes the relationship between the angles of incidence and refraction?

a) Snell's Law

b) Newton's Law

c) Boyle's Law

d) Hooke's Law

3. Which phenomenon is responsible for the formation of rainbows?

a) Reflection

b) Refraction

b) Refraction c) Diffraction

d) Absorption

4. What is the refractive index of a vacuum?

Refractive Index

a) 0

b) 1

c) 2

d) 3

5. How does the refractive index of diamond compare to that of quartz?

a) Diamond has a higher RI

b) Quartz has a higher RI

c) They have the same RI

d) It depends on the wavelength of light

6. Which gemstone has a typical refractive index around 1.541.55?

a) Diamond

b) Sapphire

c) Quartz

d) Spinel

7. What effect does a higher refractive index have on the brilliance of a gemstone?

a) Decreases brilliance

b) Increases brilliance

c) No effect on brilliance

d) Makes the gemstone opaque

8. What is another term for single refractive materials?

Single Refractive and Double Refractive Materials

a) Anisotropic

b) Isotropic

c) Birefringent

d) Polarized

9. Which gemstone is an example of a single refractive material?

a) Calcite

b) Quartz

c) Diamond

d) Tourmaline

10. What is birefringence?

a) The dispersion of light into multiple colors

b) The splitting of light into two rays

c) The absorption of light by a material

d) The reflection of light off a surface

11. Which gemstone is known for its strong birefringence?

a) Diamond

b) Spinel

c) Calcite

d) Glass

12. What is the primary use of a gemological refractometer?

Refractometer

a) To measure the hardness of gemstones

b) To measure the refractive index of gemstones

c) To measure the weight of gemstones

d) To measure the color of gemstones

13. Which component of the refractometer provides illumination?

a) Scale

b) Hemisphere prism

c) Light source

d) Viewing eyepiece

14. What is the purpose of the calibration control on a refractometer?

a) To measure the weight of gemstones

b) To adjust the instrument for accurate RI measurement

c) To measure the color of gemstones

d) To measure the hardness of gemstones

15. Which liquid is commonly used to create optical contact between the gem and the refractometer prism?

a) Water

b) Oil

c) High RI liquid

d) Alcohol

16. What does birefringence measure?

Birefringence and Optic Sign

a) The hardness of a material

b) The dispersion of light in a material

c) The difference in refractive indices within an anisotropic material

d) The color of light emitted by a material

17. Which optic sign indicates that the extraordinary ray travels slower than the ordinary ray?

a) Optically neutral

b) Optically positive

c) Optically negative

d) Optically inactive

18. Which method is used to observe the interference pattern and determine the optic sign?

a) Polarizing filter

b) Conoscopic observation

c) Reflective measurement

d) Absorption spectroscopy

19. What is the typical birefringence of calcite?

a) 0.009

b) 0.052

c) 0.172

d) 0.200

20. What type of gemstones is the distance vision method particularly useful for?

Distance Vision Method for RI Measurement

a) Faceted gemstones

b) Opaque gemstones

c) Cabochon gemstones

d) Synthetic gemstones

21. What is the main advantage of the distance vision method?

a) It provides a quick measurement of weight

b) It avoids the need for a refractometer

c) It is nondestructive to the gemstone

d) It provides a digital reading of the RI

22. Why is a monochromatic light source used in the distance vision method?

a) To measure the dispersion of the gemstone

b) To measure the specific gravity of the gemstone

c) To avoid dispersion and ensure accurate readings

d) To change the color of the gemstone

23. What is the purpose of using contact liquid in the distance vision method?

a) To clean the gemstone

b) To enhance the gemstone's color

c) To create good optical contact between the gem and the prism

d) To weigh the gemstone

24. What is the measure of how much light bends when it enters a material?

General Knowledge

a) Reflection

b) Refraction

c) Dispersion

d) Absorption

25. Which gemstone has a typical refractive index around 2.42?

a) Diamond

b) Quartz

c) Sapphire

d) Spinel

26. What is the optical property that helps in identifying gemstones by their RI?

a) Hardness

b) Dispersion

c) Refractive Index

d) Weight

27. What happens to light when it passes from a medium with a lower RI to a medium with a higher RI?

a) It speeds up

b) It slows down

c) It changes color

d) It remains unaffected

28. Which instrument is commonly used to measure the RI of liquids and solids in gemology?

a) Spectroscope

b) Refractometer

c) Polarimeter

d) Microscope

29. What is the typical result when using a refractometer on a gemstone with a high RI?

a) The boundary line appears at a lower RI value

b) The boundary line appears at a higher RI value

c) The gemstone becomes opaque

d) The gemstone changes color

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