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Flashcards in polarising microscopy Deck (53):
1

What is unique feature of polarising microscope?

1. Standard optics, light source and condenser
2. At least two polarising filters
3. optically active specimen

2

What can be changed to standard optics and condenser?

May be specially designed and added feature

3

Give some examples of added feature on standard optics.

1. Filters incorporated into condenser lens
2. a rotating stage

4

What is two polarising filters?

1. polariser
2, analyser

5

What system is polariser used in?

Illumination system

6

What system is analyser used in?

Imaging forming system

7

Where is polariser ?

In or near the condenser

8

Where is analyser

In or near the objective

9

How can polarising microscope used for analysis?

When additional filters are used: quarter wave plate

10

What are these filters always made of?

Polaroid
Calcite( but inferior)

11

How to determine whether the light is polarised or unpolarised?

The direction of oscillation of photons determine

12

What is unpolarised light?

Photon oscillations in any direction
->random

13

What is polarised light?

Photon oscillations in just one plane
->any single plance

14

What is the properties of optically active substances?

1. Transparent substance
2. Convert unpolarised light into plane polarised light

15

What are two beams of plane polarised light emitted called?

E rays
O rays

16

What is direction of polarization of E & O rays?

90 degrees to each other

17

What are alternative terms for "optically active"?

-double refraction
-birefringence
-anisotrophic

18

Give examples of optically active substance ?

Calcite

19

What should known about optically active substance?

They transmit two separate beams of plane polarised light (called E ray& O ray) with planes of polarisation at 90 degree

20

How is Polaroid unique in optically active substances?

Only transmits light which is polarised in one plane

21

Why it is possible Polaroid only transmit one plane polarised light?

O ray is absorbed

22

Are there always two plan of polarised light?

No, some separation may not be visible without special apparatus
(small angle of separation of E&O rays)

23

What is the isotrophic substance?

Minority which are not optically active

24

What do polarising filters made of Polaroid do?

Convert unpolarised light to plane polarised light in the direction similar to optic axis

25

What determine direction of polarization of unpolarised light transmitted by Polaroid?

Direction of polarization determined by the optic axis

26

How the transmitted light linked to optic axis?

Transmitted light parallel to the optic axis

27

What is depends of relationship described ?

--The directing of polarization of the indent light
---directing of the optic axis of the Polaroid

28

How is relation relevant to the polarising microscope?

->It uses two filters
->Polariser directs plane polarised light onto the specimen
->then passes to the analyser

29

What happens to incident light parallel to optic axis after transmission thru polaroid?

-no change in plane of polarization
--without change of intensity

30

what happens to incident light not parallel to optic axis after transmisstion thru polaroid?

-change in direction of polarization
-loss of intensity

31

what happens to incident light at right angles to optic axis?

no transmission of light

32

what is three optically actve substance in the polarsing microscope?

-polariser
-specimen
-analyser

33

How is poloariser and analyser are set up?

with optic axes at 90 degree: crossed polars

34

what is principle of the polarising microscope?

-background light passed polariser in condenser (same direction as optic ais) but unable to pass analyser in ocular (optic axis is 90degree)
-light repolarised by sepcimen passes through analyser

35

how to set up the polarsing microscope?

1. add poliarser and analyser
2. set up crossed polars
3. use an opticlaly active specimen

36

what does "corssed polars? mean?

set up with optic axes of polariser and analyser at 90 degree

37

How to recognize cross polars?

recognize by dark background called extinction

38

How does opticlally active specimen work to pproduce dark background?

repolarize the plane polarized background light

39

how does double refraction happen to optically active substance other than polaroid?

-they produce two transmitted beams of plane polarised light
- light coming from a singel point object splits a and form two images

40

is double refraction always obvious?

no, as teh separation of the E &O ray is often very small

41

what is anle of separation dependent?

variable angel of separation depend on the :
-angle of incidence
-relation to the optic axis

42

what is birefringence?

the sepration of E & O rays

43

what if angle of incidence parallel to optic axis?

No E&O ray separation

44

what if angle of incidence at right angles to optic axis?

produce maimum birefringence

45

three categories of birefringence of specimens?

1. crystaline birefringnece
2. form biferingence
3. stress biferingence

46

what types of specimens have crystaline birefringence?

crystals except the cubic form

47

what is cubic form?

have symmetrical arrangement of atoms within srystal lattice

48

examples of crystaline birefringence specimens?

-calcite
-picric acid : orthorhomic crystaline form

49

what types of speicmens have form birefringence?

specimens with a regular or repeating pattern of substructure

50

what is regular or repeatingi pattern of substructure?

filaments
membranes
macromolecules

51

examples of form birefringence specimens?

-striated muscle: parallel rod/ elongated structure
-molecoles in starch grains: radial rod/elongated structure
-myelin (whorled membrane): tagential elongated structures
-mica: plate
-polaroid

52

what types of speicmens have stree birefringence?

specimen with a temporary alighment of their substructure due to stress

53

examples of form birefringence specimens?

glass under stress: car windscreen