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Optics > 3. Refraction of Light > Flashcards

3. Refraction of Light Flashcards

1
Q

define refraction

A

chane in driection of light when is passess from one transparent medium into another of different optical density

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2
Q

what impacts the velocity of light

A

density of the medium it travels through

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3
Q

denser medium

A

slower light

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4
Q

what happens when a beam of light strikes a more dense medium obliquelys

A

edge of a beam which arrives first is slowed down when entering the medium
the other side continues at the same speed
when the other side hits the medium it is deviated towars the normal as it enters

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5
Q

Optical density

A

comparison of velocity of light in a vacuum vs in the medium

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6
Q

what is the measurement of optical density

A

measurement - absolute refractive index (n) of the medium

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7
Q

absolute refractive index =

A

velocity of light in a vacuum / velocity of light in medium

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8
Q

air and vacuum with the refractive index

A

as optical density in air as a medium is neglible under normal conditions
air = vacuum

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9
Q

refractive index of air

A

1

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10
Q

refractive index of water (incl aqeuous)

A

1.33

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11
Q

refractive index of cornea

A

1.37

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12
Q

refractive index of crystallinelens

A

1.386 - 1.406

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13
Q

refractive index of crown glass

A

1.52

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14
Q

refractive index of flint glass

A

1.6

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15
Q

refractive index of diamond

A

2.5

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16
Q

how can you measure refractive index

A

using a refractometer

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17
Q

on entering an optically dense medium from a less dense medium

A

light is deviated towards the normal

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18
Q

what governs / influences the angle of incidence and reflection

A

refractive indices of the media according to Snell’s law

19
Q

Snell’s law

A

incident ray, refracted ray and normal all lie in the same plan
angles of incidence and refraction are related to the refractive index of the media

20
Q

Snell’s law equation

A

medium1x n x medium 2 = sin i / sin R

where n is the refractive index

21
Q

Snell’s law equation in air to glass

A

air x N x glass = sin i / sin r

22
Q

if the interface is between two denser mediums (glass and air) then the value of n for that interface can be calculated b

A

water N glass = n glass / n water

23
Q

if passing from medium 1 to medium 2 the index of refraction can be given by

A

1n2 = n2 / n1

24
Q

What happens when light passes air -> glass -> air

A

Air -> glass = deviated towards the normal

glass -> = deviated away from the normal

BUT overall it is laterally displaced

25
Q

light passing across a curved interface between two media of different refractive indices

A

obeys snell’s law

26
Q

a convex spherical cruved surface

A

causes parallel light to conver or diverege

27
Q

convex curved surface cause CONVERGENCE if

A

n1 < n2

if the media passing to is greater than from
e.g. air : cornea

28
Q

convex curved surface cause DIVERGENCE if

A

n1 > n2

if the media passing to is LESS than from
e.g. glass : air

29
Q

refracting power of a surface formula

A

surface power = (n2-n1) / r

where r is the radius of the curvature of the surface in METRES

30
Q

what is refracting power measured in

A

dioptres

31
Q

surface power is positive for

A

converging surfaces

32
Q

surgace power is negative for

A

diverging surfaces

33
Q

example of a refracting surface

A

anterior surface of the cornea

34
Q

objects situated in an optically dense mediua appear

A

displaced when viewed from a less dense medium

this is due to refraction

35
Q

What happens to rays emerging from a denser medium

A
  1. strike at 90 degree and leave undeviated
  2. strike at less than 90 degree and are refracted
  3. meets at the citical angle and run parallel with the inferface
  4. less than critical angle and are internally reflectid
36
Q

how is the critical angle determined

A

by the refractive indcies of thhe media and can be calculated using Snell’s law

37
Q

critical angle for tear film / air interface

A

48.5 degrees

38
Q

critical angle for crown glass / air interface

A

41

39
Q

example of how total internal refleciton is used pratically

A

fibre opitc cables

40
Q

what prevents visulation of the angle of the anterior chamber and peripheral retina

A

total internal reflection

41
Q

how to overcome total internal reflection when examining the ey

A

use a contact lens that has a HIGHER refractive indice than the eye and filling the space between the eye and the lens

changes the refracting surface to allow visulaision of the angle of the anterior chamber

42
Q

dispersion of light

A

light of shorter waves are deviated more than longer

blue more than red

43
Q

dispersive power

A

indicate by the anlge formed between red and blue light leaving (with yellow in betwee)

44
Q

dispersive power and refractive index

A

are NOT related

Optics (18 decks)

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