Class 11 Physics Units and Measurements Measuring very small distances

Measuring very small distances

To measure distances as low as size of a molecule, electron microscopes are used. These contain electrons beams controlled by electric and magnetic fields.

  • Electron microscopes have a resolution of 0.6 Å or Agstroms.
  • Electron microscopes are able to resolve atoms and molecules while using tunneling microscopy, it is possible to estimate size of molecule.

Estimating size of molecule of Oleic acid

The steps followed in determining the size of molecule are:

  • Dissolve 1 cm3 of oleic acid in alcohol to make a solution of 20 cm3.Take 1 cm3 of above solution and dissolve in alcohol to make a solution of 20 cm3 Concentration of oleic acid in the solution will be (1/(20x20)) cm3.
  • Sprinkle lycopodium powder on the surface of water in a trough and put one drop of above solution. The oleic acid in the solution will spread over water in a circular molecular thick film.
  • Measure the diameter of the above circular film using below calculations.
  • If n –Number of drops of solution in water, V – Volume of each drop, t – Thickness of the film, A – Area of the film

Total volume of n drops of solution = nV cm3

Amount of Oleic acid in this solution = nV(1/(20x20)) cm3

Thickness of the film = t = Volume of the film / Area of the film

t =  nV/(20x20A) cm

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