Chapter 3: Refraction

Question 1

What is the absolute refractive index of a medium

Answer 1

Velocity of light in a vacuum/ velocity of light in the object.
Determined using a refractometer.

Question 2

What is the refractive index of air

Answer 2

1

Question 3

WHat is the refractive index of the cornea

Answer 3

1.37

Question 4

Describe snells law

Answer 4

Question 5

How to calculate the index of refraction when light passes from material x to material y

Answer 5

Refractive index of x/ refractive index of y

Question 6

When light passes obliquely from air to glass to air at an oblique angle, what happens?

Answer 6

Question 7

True or false
All light incident on a lens is refracted

Answer 7

False, some is reflected

Question 8

What is the refractive power or vengeance power of a curved interface

Answer 8

Question 9

When is the refractive power denoted as positive or negative

Answer 9

If light is converging, it is positive. If light is being diverged, it is negative

Question 10

How does genioscopy work

Answer 10

COrnea air interface causes total internal reflection of light from the angles. Contact lens of genioscopy removes that interface and so light is refracted allowing visualisation of the anterior chamber angle (gonioscopy) and peripheral retina (three-mirror).
the air cornea interface is replaced by cornea, saline, high refractive power lens interface.

Question 11

In refraction, which wavelengths of light are deviated the most?

Answer 11

Short wavelengths ie blue light

Question 12

True or false, the refractive index of a material does not relate to its dispersive power (ability to split light)

Answer 12

True

Question 13

How do you calculate the dispersive power of a medium

Answer 13

The angle formed between the red and blue light around the yellow (Fig. 3.12) indicates the dispersive power of the medium (cf. chromatic aberration, p. 89). This is not related to the refractive index of the material.

Question 14

True or false:

The refractive index of any medium differs slightly for light of different wavelengths.

Answer 14

True!

Question 15

Describe the formation of a rainbow

Answer 15

1. White light is dispersed into the spectrum and undergoes total internal reflection. The observer receives only a narrow pencil of rays from each drop, i.e. only one colour. Thus you see the rainbow from different drops showing different colours. Usually, violet is at the bottom and red is at the top.
   Secondary rainbows are the opposite.