Chapter 2.2 - Magnification and Calibration

Question 1

Definition of magnification

Answer 1

How many times larger the image is that the actual size of the object being viewed.

Question 2

How can you change the magnification on a compound light microscope

Answer 2

Interchangable objective lenses

Question 3

Definition of resolution

Answer 3

ability to see individual objects as separate entities.

Question 4

What affects resolution

Answer 4

Diffraction of light as it passes through samples (and lenses).

Question 5

Definition of diffraction

Answer 5

Tendency of light waves to spread as they pass close to physical structures (such as those present in the specimen that is being studied)

Question 6

How does diffraction affect resolution

Answer 6

Structures present in specimens are v close to eachother.
Light reflected from individual structures can overlap due to diffraction.
Structures are no longer seen as separate entities.
Detail is lost.
Optical microscopy structures closer than half a wavelength are resolved.

Question 7

How to increase resolution

Answer 7

Use beam of electrons.
Wavlength is thousands of times smaller than lights
Still diffracted but shorter wavelength means individual beams need to be much closer before they overlap.
Objects that are smaller and closer can be seen separately without diffraction bluriing the image

Question 8

Formula for magnification

Answer 8

size of image/actual size

Question 9

Use of an eyepiece graticule and why is it necessary

Answer 9

Measure the size of a sample under a microscope. Calibrates the different lenses of a microscope using a stage micrometer. True magnification varies slightly from magnification stated.

Question 10

What is an eyepiece graticule

Answer 10

glass disc marked with a fine scale of 1 to 100. No units and remains unchanged whichever objective lens is in place. Relative size of divisions increases with magnification. Scale is calibrated using slide micrometer.

Question 11

What is a stage micrometer

Answer 11

Microscope slide with accurate scale in micrometers engraved on it. 100 divisions = 1mm so 1 division = 10micrometers

Question 12

Calibrate a x4 objective lens

Answer 12

1. Line up the stage micrometer and eyepiece graticule and get in focus
2. Take reading from the scales
   1 graticule division = number of micrometres/number of graticule divisions
   graticule divisions x magnification factor = measurement