lesson 4 - microscopes

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?