Lesson 4 - Microscopes

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<ul><li> 1. Microscopes http://news.nationalgeographic.com/ news/2008/10/photogalleries/best- microscope-photos/photo2.htmlThis little guy is made of CO molecules arranged on a platinum surfacewith the help of a scanning tunnelling microscope</li></ul> <p> 2. Learning Objectives:explain and distinguish between resolution andmagnification with reference to light microscopy andelectron microscopy 3. Magnification vs. ResolutionMagnification is howResolution is themuch bigger a sampleability to distinguishappears to be under the between two points onmicroscope than it is inan image - the amountreal life.of detail. e.g. if two objectsTotal Magnification = objectiveare less thanmagnification x eyepiece magnification 200nm apart they are seen as one object.Increasing the magnification does not increase the resolution of the image!! 4. Invention of microscopeLight Microscope http://sciencevideos.wordpress.co m/2008/01/26/cell-theory/Resolution: 200nm Therefore any images closertogether than 200nm will be seen as1 objectDue to magnitude of thewavelength of light2 objects can only be seen if lightcan pass between themHuman eye resolution = 100mMagnification: x4, x10,x40x100 (oil immersion) 5. Electron microscopes 6. Generates a beam ofelectrons (0.004nmwavelength) Distinguishes betweenobjects 0.2nm apart.How is this different froma light microscope?Uses magnets instead Blood clot: platelets spin out a meshof lenses to focus the of fibrin.beam onto the specimen Taken from a scanning electron microscopeImage is projectedonto photographicpaper to make a greyscale image(Black &amp; whiteElectronmicrograph) 7. TransmissionScanning Electron ElectronMicroscopeMicroscope (TEM)(SEM) Electron beam passes Electrons dont passthrough a thin samplethrough the specimen.Electrons pass through They bounce off thethe denser parts lessspecimen.easily contrast 3D viewImage is 2D Magnification is x 100 Magnification is x 500 000000 http://www.youtube.com/watch? v=lrXMIghANbg 8. Electron microscope: advantages and disadvantagesAdvantages:Resolution is 0.1nmDetailed images or organelles3D images-shows contours(SEM)Disadvantages:Electron beams deflected byair molecules - vacuumneeded.ExpensiveSkill &amp; training needed 9. Coloured electron micrographs Electron micrographs are always black, white &amp;grey when they are producedColours can be added afterwards usingcomputer software=false colour electronmicrographs 10. What can we see with a microscope? 11. LIGHT, SEMor TEM?</p>