Principle of Light Microscopy 
                        Light microscope is also called an optical microscope. 
                        It  is  an  instrument which uses the visible light to enlarge the tiny specimens through 
                         microscopic lens.  
                        There  are  two  types  of  light  microscope,  simple  microscope  has  one  lens  with  low 
                         magnification and the compound microscope has two lenses (objective and eye piece) 
                         with higher magnification. 
                        Parts of light microscope 
                             1.  Ocular/Eyepiece  is  present  towards the  viewer.  It  converts  the  real  image  of 
                                 object into virtual image. It may be a combination of more than two lenses. 
                             2.  Lens tube is of about 160 mm length and holds the eyepiece. 
                             3.  Objective lens is present towards the object. It assembles the light reflected from 
                                 the object at a place and produces a real image of object. 
                             4.  Objective revolver consists of objective lenses of different magnifying power. 
                             5.  Stand is attached with all components of microscope and it keeps them together. 
                             6.  Clip holds the object in place. 
                             7.  Stage is the place where object is kept for observing. 
                             8.  Condenser focuses the rays of sunlight on the object. 
                             9.  Fine and coarse adjustments control the distance between object and objective. 
                                 They are used to produce sharp image of object. 
                             10. Luminous-field diaphragm controls the diameter of light coming from light 
                                 source. 
                             11. Light  source  is  the  LED  bulb  used  to  illuminate  the  object.  The  older 
                                 microscopes used concave mirror to focus the sunlight on the object to make it 
                                 visible. 
                             12. Base supports the microscope. 
                                  
                        Working principle- The light source illuminates the object. The first image of the object 
                         is  formed by objective lens which is a real, inverted and magnified image. The image 
                         formed by the objective functions as the object for eyepiece, which produces the final, 
                         virtual  and  magnified  image.  In  this  way,  the  final  image  produced  is  inverted  with 
                         respect to the object. 
                                                                                               
                                         Light microscope (Image Source- Microscopeworld) 
                  
                                                  Principle of Electron Microscopy 
                        The first electron microscope was made by a German engineer, Ernst Ruska in 1931. 
                        It  uses  the  beam  of  accelerated  electrons  to  visualize  the  specimens  and  has  a  high 
                         resolution. 
                        Parts of Electron Microscope 
                             1.  Electron gun is heated tungsten filament which produces the beam of electrons. 
                             2.  Electromagnetic  lenses-  Condenser  lens  directs  the  electron  beam  towards the 
                                 specimen. The electron beam coming out from specimen goes through objective 
                                 lens. The projector or ocular lens produces the final magnified image. 
                             3.  The specimen holder is made up of thin layer of carbon held by metal grid. 
                             4.  The  final  image  is  obtained  on  fluorescent  screen,  below  which  a  camera  is 
                                 present to capture the image. 
                        The working principle of electron microscope is discussed as follows: 
                         The beam of electrons are produced from the electron gun is focused on the specimen 
                         through two sets of condenser lens. An accelerating potential is applied between filament 
                         and anode to move the electrons downwards. The specimen to be observed is kept as thin 
                         section of 20-100 nm on specimen holder. The beam of electrons goes through specimen; 
          the denser regions scatter more electrons on the screen than the lighter regions. The beam 
          of electrons scattering from specimen passes through objective lens to create magnified 
          image which is further magnified by ocular lens. 
                                          
                 Electron Microscope (Image Source- Microbenotes)