Microscopy Flashcards
What is the object in microscopy?
The material that is put under a microscope
What is the image in microscopy?
The appearance of the object when viewed under the microscope is the image
what is the resolution?
The minimum distance apart that two objects can be in order for them to appear as separate items. The greater the resolution, the greater than clarity
How do light microscopes work?
The light rays pass through a specimen and are focused by the objective lens and eyepiece lens to form an image
What is the limitation of light microscopes?
They have poor resolutions because of the long wavelength of light. Can only distinguish between two objects if they are 0.2 micrometers or further apart
How do electron microscopes work?
The use a beam of electrons. An electromagnet is used to focus the beam of electrons onto the specimen. They have a shorter wavelength so can distinguish two objects as close as 0.1 nano meters apart. (2,000,000x better than light microscopes)
What are the types of electron microscope?
transmission electron microscope (TEM) and scanning electron microscope (SEM)
What are the limitations of the TEM and SEM?
- A complex staining process
- Image is in black and white
- Image may contain artefacts (things that result from the way the specimen is prepared)
- specimen must be very thin (TEM)
- must be done in a vacuum so can’t observe living specimens
How does TEM work
An electron beam is passed through an extremely thin section of the specimen. And is focused by an electromagnet. Dense parts of specimen absorb electron beam and appear dark and vice Versa, creating an image.
Why can’t the max resolving power of TEM be achieved
We would need a very high energy electron beam and this may destroy the specimen.
Difficulties preparing the specimen will limit the resolution we can achieve
How does SEM work
-beam of electrons onto surface of specimen from above not below
-beam passed back and forth across portion of specimen in a regular pattern
-electrons scattered by specimen
-then can build up 3D image by a computer analysis based on pattern and secondary electrons produced
