Lab #1

Question 1

Define transmission electron microscopy (TEM)

Answer 1

Electrons pass through the cell, so you can see detailed images of its inside

Question 2

Define scanning electron microscopy (SEM)

Answer 2

Electrons bounce off the cell, so you can capture detailed images of its surface

Question 3

Define ocular lens

Answer 3

Binocular lenses to which you place your eyes for viewing the specimen. These lenses have a set magnification of 10x

Question 4

Define objective lenses

Answer 4

Three or four lenses mounted on a turret that provide the major magnification power of the microscope. These lenses are rotated into place immediately above the specimen. Typical magnification powers usually include 4x, 10x, 40x, and 100x. In concert with the ocular lenses, these objective lenses yield total magnification powers of 40x, 100x, 400x, and 1000x

Question 5

Define revolving turret

Answer 5

A mechanism allowing movement of the different objectives into place above the specimen

Question 6

Define stage

Answer 6

Flat plate on which the specimen is placed. Light passes from the condenser through a hole in the plate and then through the specimen on a microscope slide.

Question 7

Define slide clamp

Answer 7

Holds the glass slide with the specimen in the correct place for observation, allowing the entire slide to be moved by the slide manipulator

Question 8

Define slide manipulator

Answer 8

Through the use of a system of gears, the manipulator moves the slide clamp holding the slide. This allows for smooth movement of the slide, allowing precise location of different parts of the slide

Question 9

Define condenser

Answer 9

A series of lenses that focuses light traveling from the light source on the specimen. Depending on the type of microscope, condensers can provide multiple settings. Settings often seen include bright field (used most often), dark field (providing excellent illumination of the edges), phase contrast (enhancing poorly contrasting objects), and many other options

Question 10

Define iris diaphragm

Answer 10

Allows for the reduction of or expansion of the amount of light passing from the condenser to the specimen

Question 11

Define coarse focus adjuster

Answer 11

Allows for focusing the image on lower power objective lenses (4x or 10x lenses). Often used to quickly scan specimens and focus in on interesting items on the slide

Question 12

Define fine focus adjuster

Answer 12

Allows for focusing the image on higher power objective lenses (40x or 100x lenses). Since the working distance of these higher power lenses is relatively small, the fine focus is the only focus that should be used with these; use of coarse focus on the higher power lenses could lead to lens damage

Question 13

Define rheostat

Answer 13

Power control that increases or decreases the voltage applied to the light source, increasing or decreasing the brightness. Generally ranging from 0 to 10. Properly stored microscopes should always have their rheostats adjusted to 0 to minimize possible bulb filament breakage if the power is switched on with too high an initial voltage.

Question 14

Define power switch

Answer 14

Controls the application of electrical power to the rheostat.

Question 15

Define light source

Answer 15

Generally a tungsten filament bulb

Question 16

Define magnification

Answer 16

The relative enlargement of the image. Total magnifications are calculated by multiplying the magnification of each lens the light passes through after passing through the specimen. For the microscopes in this lab total magnification is calculated by multiplying the power of the objective and ocular lenses

Question 17

Define resolution

Answer 17

The ability of a microscope to enable visualization of two closely spaced points on a specimen. In practice, known as the resolving power of a microscope, the lower the resolving power the better the resolution

Question 18

Define resolving power

Answer 18

Defined as the smallest distance between two points where those two points are clearly visible. Mathematically related as follows: RP = wavelength / (NAobj. + NAcond.), where NA is the numerical aperture of either the objective or condenser lens systems. Numerical aperture = n (Sin0), where n is the lens refractive index and 0 is the angle from the center of the beam of light as it passe through the specimen to the outer edge of the objective lens.

Question 19

Define refraction

Answer 19

The bending of light

Question 20

Define refractive index

Answer 20

Different substances that will transmit light have different refractive indices. Air has a refractive index of 1.0, glass is about 1.5, and immersion oil is very close to 1.5

Question 21

Define immersion oil

Answer 21

A highly purified oil used to fill the space between the specimen and the objective and condenser lenses. Usually, for the sake of keeping the microscope clean, the oil is not added to the bottom of the slide. When added the oil displaces the air, reducing refraction of light passing through the specimen. This decreases the resolving power of the lens system, increasing the microscope’s resolution. We only use this on 1000x

Question 22

Define focal length

Answer 22

The specific working distance of the lens system when the specimen is in focus to the observer

Question 23

Define parfocal

Answer 23

A geometric property of a lens system and microscope allowing for nearly focused images when switching from a focused lower objective magnification to a higher power lens (which should be in focus with minimal movement of the fine focus).

Question 24

Define working distance

Answer 24

The space between a focused objective lens and the surface of the slide. For lenses on typical microbiology laboratory microscopes the working distances are as follows: 4x, about 2cm; 10x, about .5cm; 40x, about .4mm; and 100x, about .1mm