Microscopy

Question 1

Magnification equation

Answer 1

M=I/A
M= scale line measured/scale line given

Question 2

What is resolution?

Answer 2

the smallest distance between 2 particles which allows them to be distinguished from one another

Question 3

Why is the light microscope magnification and resolution limited?

Answer 3

The wavelength of invisible light is too long and the thickness of the sample

Question 4

Why does the electron microscope have a greater resolution?

Answer 4

they have a shorter wavelength than visible light so you can distinguish between objects

Question 5

Features of an SEM

Answer 5

Scanning electron microscope
- electrons are beamed onto surface and electrons are scattered depending on the contours (sheet/wave)
-3D- lower resolution than TEM
- can’t see internal structures
- specimen can be thick as electrons aren’t passed through

Question 6

Features of TEM

Answer 6

Transmission electron microscope
- fine beam of electrons that transmit/ pass through specimen
- denser parts of specimen absorb more electron so appear darker
-2D
- can see the internal structures / organelles - high resolution
- thin specimen stained and placed in vaccuum

Question 7

How do you prepare a microscope slide?

Answer 7

1.) Pipette a small drop of water onto the centre of the slide
2.) Use tweezers to place a thin section of the specimen on top of the water drop - needs to be thin to allow water through to see it clearly
3.) Add a drop of stain to highlight the organelles
4.) Add a coverslip - stand the slip upright on the slide and tilt and lower it so it covers the specimen - air bubbles will obstruct your view

Question 8

What is magnification?

Answer 8

how many times larger the image is compared to the object

Question 9

How do you work out the size of an object views with microscope?

Answer 9

use a graticule
the graticule must be calibrated each time you change the magnification to work out what the distance is between each division represents at that magnification

Question 10

How do you get from mm to micrometers (μm)?

Answer 10

x 1000
1mm = 1000μm

Question 11

How do you get from mm to nanometers (nm)?

Answer 11

x 1000000
1mm = 1000000nm

Question 12

How can you calibrate?

Answer 12

line up stage micrometer and graticule whilst looking through eyepiece and count how many divisions on the graticule fit into 1 division on micrometer scale - each division on micrometer is 10μm so calculate what 1 division is

Question 13

What are the features of an optical microscope?

Answer 13

• beam of light condensed to create the image
• poor resolution as wavelength of visible light is too long
• low magnification -if sample is too thick light cant be let through
• colour images
• view living specimens

Question 14

What are features of an electron microscope?

Answer 14

• beam of electrons condensed to create image - electromagnets used to condense beams
• greater resolution as has shorter wavelength than visible light
• higher magnification
• black and white images
• view non living specimens