The Electron Microscope

Question 1

What are the two main advantages of an electron microscope

Answer 1

The electron beam has a very short wavelength and the microscope can therefore resolve objects well, it has a high resolving power

As electrons are negatively charged the beam can be focused using electromagnets

Question 2

What are the 2 types of electron microscopes

Answer 2

Transmission Electron microscope

Scanning electron microscope

Question 3

How does TEM work

Answer 3

It uses electromagnets to focus a beam of electrons which is then transmitted through the specimen. Denser parts of the specimen absorb more electrons, which make
s them look darker on the image you end up with

Question 4

How does SEM work

Answer 4

Scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image. Gives excellent 3D images

Question 5

Which has a better resolution TEM OR SEM

Answer 5

TEM

Question 6

What’s the advantages and disadvantages of a light microscope

Answer 6

+ can be used to view live whole specimens under low magnifications

-low resolution does not allow much subcellular detailed to be observed

Question 7

What’s the advantages and disadvantages of TEM

Answer 7

+ uses beams of electrons
Short wavelength
High resolution so more detail

-electrons scattered
Must be in a vacuum therefore cannot examine living cells
Lots of preparation 
May alter appearance
Very thin specimen 
Black n White images

Question 8

Advantages and disadvantages of SEM

Answer 8

+creates 3D effect of image of the surface of the specimen
Can be used on thick specimens

-specimen are always dead and may contain artefacts as a result of preparation techniques
Give lower resolution images

Question 9

Explain how the electron microscope is able to resolve objects better then the light microscope

Answer 9

The EM uses a beam of electrons that has a much smaller wavelength then light

Question 10

Explain why specimens have to be kept in a near vacuum in order to be viewed effectively using an electron microscope

Answer 10

Electrons Are absorbed by the molecules in air, and if present, this would prevent the electrons reaching the specimen

Question 11

In practice, the theoretical resolving power of an electron microscope cannot always be achieved. Explain why not.

Answer 11

The preparation of the specimens may not be good enough. A higher energy electron beam is required and this many destroy the specimen