Module 2

Question 1

What is the focal point?

Answer 1

The point at which parallel light rays converge.

Question 2

What is focal length?

Answer 2

The distance from the centre of the lens to the focal point (lens to focused light).

Question 3

What is the focal plane?

Answer 3

The vertical plane the plane of focus lies in.

Question 4

What is working distance?

Answer 4

The distance from the specimen to the objective lens.

Question 5

How does working distance relate to magnification?

Answer 5

The shorter it is the greater the magnification.

Question 6

What is the depth of field?

Answer 6

The range in which the object is in focus.

Question 7

What lenses have a narrower range of focus?

Answer 7

Higher magnification lenses.

Question 8

What is the conjugate foci?

Answer 8

The object and its formed image.

Question 9

How does focal length change the formed image? (Eg. If it’s 2F what does it look like? Etc.)

Answer 9

> 2F- real, smaller, inverted

2F- real, same size, inverted

2F-1F- real, magnified, inverted

1F- rays emerge parallel (no image)

Question 10

What two lenses does a compound microscope combine?

Answer 10

Objective and ocular

Question 11

What are the working distances of the lenses in the compound microscope?

Answer 11

Objective: 1F-2F

Ocular:

Question 12

What is the object the ocular lens of a compound microscope focuses on?

Answer 12

The real image created by the objective.

Question 13

How is total magnification determined?

Answer 13

Multiplying the magnification of the objective and ocular lenses.

Question 14

What causes aberrations?

Answer 14

Refraction

Question 15

What are the different kinds of aberrations and why do they form?

Answer 15

Chromatic- different wavelengths have different focal points so colours are distorted

Spherical- light in the centre doesn’t refract as much as the periphery which appears blurred

Question 16

What are the lenses that correct for aberrations?

Answer 16

Achromatic- red and blue

Semiapochromats- red, blue and some green

Apochromats- red, blue and green

Plan- produce flat fields of view

Question 17

How do plan- lenses correct?

Answer 17

Combinations of convex and concave lenses.

Question 18

What are the parts of the compound microscope?

Answer 18

Light source (radiant field diaphragm)
Condenser assembly (aperture diaphragm and lens system)
Stage assembly
Nosepiece/objectives
Body tube
Oculars

Question 19

Objectives do not need to be reduced when increasing magnification because why?

Answer 19

They are parfocal.

Question 20

What is mechanical tube length?

Answer 20

Distance from the top of the ocular to the objective junction.

Question 21

What is optical tube length?

Answer 21

The distance from the objective lens and the focal plane of the ocular.

Question 22

What is the common range of viewing field size?

Answer 22

19-22mm

Question 23

What does the amount of refraction depend on?

Answer 23

Angle of incidence- angle at which light strikes the surface

Refractive index- expression of medium density

Question 24

When light enters a more dense medium is bends toward what?

Answer 24

Normal (90°)

Question 25

What is the critical angle?

Answer 25

In a dense medium leaving to a less dense medium, the angle at which total internal reflection occurs.

Question 26

What types of mediums have higher refractive indexes?

Answer 26

More dense mediums

Question 27

What is the refractive index of immersion oil and what is its purpose?

Answer 27

1.52 (same as crown glass) Prevents the loss of light rays because the refractive index doesn't change so the rays are less scattered. More light makes it to the lens.

Question 28

What is resolution?

Answer 28

The ability of a lens to discern fine detail (tell two points apart).

Question 29

What is resolution dependent on?

Answer 29

Wavelength and numerical aperture

Question 30

What is the equation to calculate resolution?

Answer 30

R = wavelength/2NA

Question 31

How does wavelength affect resolution?

Answer 31

The shorter the wavelength the more separation. But it is a range (visible light).

Question 32

What is numerical aperture?

Answer 32

The ability of a lens to gather light.

Question 33

How does numerical aperture affect resolution?

Answer 33

The bigger the bundle of light (NA) the better the resolution.

Question 34

What does numerical aperture depend on?

Answer 34

The refractive index of the medium.

Question 35

What objective lenses have higher numerical apertures?

Answer 35

100x is the greatest (increases with mag)

Question 36

What does setting Kohler do?

Answer 36

Matches the NA of the condenser to that of the objective to provide the best resolution.

Question 37

What is the optimum useful magnification?

Answer 37

The highest magnification and resolution, any magnification higher loses resolution (empty mag)

Question 38

How is useful and empty magnification calculated?

Answer 38

Useful- NAx10^3 > total mag Empty- NAx10^3

Question 39

What markings are found on the objective lenses?

Answer 39

``` Magnification NA Tube length Coverslip thickness Oil immersion Aberration corrections ```

Question 40

What working distance are infinity corrected objectives focused at?

Answer 40

1F

Question 41

What does an infinity lens allow the use of?

Answer 41

Filters and polarizers

Question 42

What must an infinity lens be used with?

Answer 42

A microscope with a tube lens.

Question 43

What two types of lenses are there and how do they affect light?

Answer 43

Convex- converge rays, magnification Concave- diverge rays