microscopes and magnification Flashcards
what is magnification and resolution
-Magnification is how many times bigger an image appears
-Resolution is the ability to determine between 2 separate points
equation of magnification
-I AM (Image size=Actual size x Magnification)
-usually measured in mm
conversions
cm millimeter micrometer nanometer
x10. x1000 x1000
How does a light microscope work
-Light microscope uses lenses to project a magnified image of an object onto the eye
Why do light microscope have low resolution
-Because of the long wavelengh of light rays, meaning that a light microscope can only distinguish between 2 objects if they are 0.2 micrometers apart
How do electron microscope work
- An electron microscope exposes a specimen to electrons instead of light
Why do electron microscopes have a higher resolution and magnification
-Electrons have a much shorter wavelenght than light
How do scanning electron microscopes work
-Specimens are coated with a thin layer of metal such as gold, platinum or tungsten to improve conductivity and contrast.
-The electrons are reflected from the surface of the specimen producing a 3D image.
How do transmission electron microscope work
• Very thin slices are made, and then stained with heavy metals.
• Electrons don’t pass through the heavily- stained parts because they are absorbed
• Those that pass through are focused by electromagnets onto a fluorescent screen or photographic plate.
• 2D images only
Limitations of Electron microscopes
• Cannot look at living material as in a vacuum • Image is only 2D (TEM)
• Specimen must be very thin (TEM)
• Specimens take a lot of time to prepare
• Artefacts present
what is an eyepiece graticule
• It is a glass disc which is within the eyepiece. The glass disc has scale on to it, so you can line it onto your object.
why dont you have to change the eyepiece graticule at different magnification
-The eyepiece graticule remains constant no matter
what magnification the cells
are viewed at.
