Give two advantages of the electron microscope

• The electron beam has a very short wavelength and the microscope can therefore resolve objects very well due to it's high resolving power.
• As electrons are negatively charged, the beamcan be focused using electromagnets.

Why is a near vacuum state needed to be created when using an electron microscope effectively?

• Electrons are abosrbed by te molecules in the air

How far can the best modern electron micorscope resolve objects better, than the light microscope?

• 0.1 nm
• 2000 times better than light microscope

What types of electron microscope are there?

• Transmission electron microscope - TEM
• Scanning electron microscope - SEM

What are the main limitations of the TEM?

• Whole system must be in a vacuum and therefore livivng specimens cannot be observed
• Complex staining process is required and even then the image is in black and white
• The specimen must be extremely thin
• Image may contain artefacts .
•  Artefacts are things that result from the way the specimen is prepared. They may appear on the finished photomicrograph but aren't part of the natural specimen. therefore it is not always easy to be sure that what we see on a photomicrograph really exists in that form. 

What does the transmission electron microscope consist of?

• It consists of an electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet

In the TEM, where does the beam pass through?

• The TEM passes through a thin section of specimen. 

Why do some parts of the specimen appear dark and others appear bright?

• Some parts of the specimen absorb the electrons and so appear dark
• Other parts allow the electrons to pass through and so appear bright

What is the resolving power of the TEM?

• The resolving power is 0.1nm

Why must the specimens be extremely thin?

• To allow the electrons to penetrate the specimen

What limitation affects the TEM and not the SEM and why?

• The specimens in the sem do not need to be extremely thin  as electrons do not penetrate

Why is the electron microscope able to resolve objects better than the light microscope?

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

Why do specimens have to be kept in a near-vacuum in order to be viewed effectively using an electron microscope?

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