lesson 4 - microscopes
TRANSCRIPT
Microscopes
This little guy is made of CO molecules arranged on a platinum surfacewith the help of a scanning tunnelling microscope
http://news.nationalgeographic.com/news/2008/10/photogalleries/best-microscope-photos/photo2.html
Learning Objectives:
explain and distinguish between resolution and
magnification with reference to light microscopy and electron microscopy
Magnification vs. Resolution
Magnification is how much bigger a sample appears to be under the microscope than it is in real life.
Resolution is the ability to distinguish between two points on an image - the amount of detail.
Increasing the magnification does not increase the resolution of the image!!
Total Magnification = objective magnification x eyepiece magnification
e.g. if two objects are less than 200nm apart they are seen as one object.
Light Microscope Invention of microscopehttp://sciencevideos.wordpress.com/2008/01/26/cell-theory/Resolution: 200nm
Therefore any images closer together than 200nm will be seen as 1 objectDue to magnitude of the wavelength of light2 objects can only be seen if light can pass between themHuman eye resolution = 100μm
Magnification: x4, x10, x40x100 (oil immersion)
Electron microscopes
Generates a beam of electrons (0.004nm wavelength) Distinguishes between objects 0.2nm apart.How is this different from a light microscope?
Uses magnets insteadof lenses to focus thebeam onto the specimen
Image is projectedonto photographicpaper to make a greyscale image(Black & white Electronmicrograph)
Blood clot: platelets spin out a mesh of fibrin. Taken from a scanning electron microscope
Transmission Electron
Microscope (TEM)
Scanning Electron Microscope
(SEM)
Electron beam passes through a thin sampleElectrons pass through the denser parts less easily – contrastImage is 2D Magnification is x 500 000
Electrons don't pass through the specimen. They bounce off the specimen. 3D view Magnification is x 100 000
http://www.youtube.com/watch?v=lrXMIghANbg
Electron microscope: advantages and disadvantages
Advantages: Resolution is 0.1nmDetailed images or organelles3D images-shows contours (SEM)
Disadvantages:Electron beams deflected by air molecules - vacuum needed.ExpensiveSkill & training needed
Coloured electron micrographs
Electron micrographs are always black, white & grey when they are producedColours can be added afterwards using computer software=false colour electron micrographs
What can we see with a microscope?
LIGHT, SEM or TEM?