Module 2: Microscopy

Question 1

Convex lenses

Answer 1

Thicker in the centre
Light rays converge
Positive lenses

Question 2

Concave lenses

Answer 2

Thinner in the centre
Light rays diverge
Negative lenses
Used to correct for aberrations

Question 3

Focal length

Answer 3

Distance from the centre of the lens to the focal point

Question 4

Working distance

Answer 4

Distance from the specimen to the objective lens

Question 5

Depth of field

Answer 5

Range in which an object is in focus

Question 6

Real image

Answer 6

Object is >1 focal length from lens
Image on opposite side of lens and can be focused on a screen
Inverted

Question 7

Virtual image

Answer 7

Object within 1 focal length
Image on same side of lens
Magnified and erect
Must be viewed through a lens

Question 8

Microscope component that magnifies the object and produces a real image

Answer 8

Objective lens

Question 9

Microscope component that magnifies the real image

Answer 9

Ocular lens

Question 10

Chromatic aberration occurs because

Answer 10

Shorter wavelengths are refracted more than longer wavelengths

Question 11

Spherical aberration occurs because

Answer 11

Light passing through the centre of the lens does not bend as much as those passing through the periphery

Question 12

Chromatic aberration causes

Answer 12

Distortion of colours

Question 13

Spherical aberration causes

Answer 13

Blurry image

Question 14

Three types of objectives with correction for chromatic aberration

Answer 14

Achromats, semi-apochromats, apochromats (best)

Question 15

Lenses that are corrected for spherical aberration have the designation:

Answer 15

Plan

Question 16

Microscope component that controls the size of the light bundle striking the specimen

Answer 16

Radiant field diaphragm

Question 17

Microscope component that focuses light on the specimen

Answer 17

Condenser assembly

Question 18

Microscope component that controls the size of the cone of light striking the specimen

Answer 18

Condenser aperture diaphragm

Question 19

Distance from the optical centre of the objective lens to the focal plane of the ocular

Answer 19

Optical tube length

Question 20

Distance from the top of the ocular to the objective/nosepiece junction

Answer 20

Mechanical tube length

Question 21

Hygenian and Ramsden are types of:

Answer 21

Oculars

Question 22

Abbe and Aplanatic-achromatic are types of:

Answer 22

Condensers

Question 23

The bending of light rays as they pass through different media is termed:

Answer 23

Refraction

Question 24

The amount of refraction depends on

Answer 24

Angle of incidence and refractive index of mediums

Question 25

Critical angle

Answer 25

The angle at which light is unable to leave a more dense medium for a less dense medium

Question 26

Resolution is dependant upon two factors:

Answer 26

Wavelength of light used | Numerical aperture

Question 27

Numerical aperture

Answer 27

Mathematical expression of the light gathering ability of a lens Higher = better resolution

Question 28

Three disadvantages to high numerical aperture lenses

Answer 28

Decreased working distance Decreased depth of field Decreased flatness of field

Question 29

Calculation of total magnification

Answer 29

mag of ocular x tube length/objective focal length

Question 30

Useful magnification

Answer 30

1000 x NA is greater than the total magnification

Question 31

Empty magnification

Answer 31

1000 x NA is less than the total magnification | The limit of useful magnification is exceeded

Question 32

Kohler illumination

Answer 32

Produces even illumination of the specimen | Matches the numerical aperture of the condenser to the objective lens