2.1 Microscopes and Magnification Flashcards
How does the optical microscope work?
- uses the wavelength of light which limits the resolution
- any objects less than 0.2μm apart will be seen as one object with a light microscope
- lenses focus rays of light and magnify the view of a thin slice of specimen
- different structures absorb different amounts and wavelengths of light
- reflected light is transmitted to the observer via the objective lens and eyepiece
What are the advantages of the electron microscope?
- the electron beam has a very short wavelength so it can resolve objects very well (high resolving power)
- electrons are negatively charged therefore the microscopes can be focused using electromagnets
Why do electron microscopes have a vacuum?
Because electrons are absorbed or deflected by molecules in the air
What are the disadvantages of the electron microscope?
- living specimens can’t be observed because there is no air in a vacuum
Why are transmission electron microscopes used?
- used to use the transmitted electrons; the electrons which are passing through the sample before they are collected
What are the limitations of the transmission electron microscope? (x8)
- offers invaluable information on the inner structure of the sample
- resolving power is 50pm
- images are 2D projections of the sample
- samples must be very thin
- images are not in colour
- electron beam passes through the specimen
- preparation is quite complex and tedious
- requires a vacuum = cannot show living structures
What are the advantages of the transmission electron microscope?
- users can magnify their samples by more than 50 million times
- electrons have shorter wavelength than light = high resolution, so ultrastructure visible
How does the scanning electron microscope work?
- uses a specific set of coils to scan the beam in a raster like pattern and collect the scattered electrons
What are the limitations of scanning electron microscopes?
- resolution is limited to ~0.5nm
- limited to 1-2 million times of magnification
- requires a vacuum = cannot show living structures
- no colour image
- only shows outer surface
What are the advantages of the scanning electron microscope?
- provides information on the samples surface and it’s composition
- electrons are reflected by the surface of the specimen
- provides a 3D image
- specimens don’t need to be thin
- little or no effort for sample preparation
- electrons have a shorter wavelength than light = high resolution
What is the object?
The material put under the microscope (specimen)
What is the image?
The appearance of it under a microscope
What is the magnification of an object?
How many times bigger the image is compared to the object
What is the equation for magnification?
size of image
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size of real object
What is resolution?
The minimum distance apart two object can be in order for them to appear as separate items
