1.4 Measuring size and calculating magnification
1.5 Electron microscopy
Eyepiece graticule
Scale inside of eyepiece used to measure specimen length
Arbitrary scale called eyepiece units (EPU)
Image size (I) = Actual size (A) x Magnification (M)
Stage micrometer
1000µm ruler used to calibrate scale on eyepiece graticule
Line up with the eyepiece graticule and find length of 1 EPU
Magnification - how large the image is compared to the original object
Resolution - the distance 2 objects must be separated by to be seen as 2 individual objects
Max. resolution of light microscope = 200nm
Objects closer than 200nm (half the wavelength) cannot be distinguished as separate
Min. wavelength of visible light = 400nm
Electron microscopes
Electrons can act as waves
Wavelength of electron = 0.005nm
TEM (transmission electron microscope)
Resolving powers
Human eye - 0.2mm
Magnification
Light microscope - x1,500
SEM (scanning electron microscope)
Specimens need to be thin
Only surfaces can be viewed
Has higher resolving power and magnification than SEM
Provides a 2D image
Provides a 3D image
SEM - x100,000
TEM - x500,000
SEM - 2-5nm
TEM - 0.05-0.1nm
Light microscope - 0.2µm