Problem No 13 Misty glass Vasiliev Andrew Team

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Problem No. 13 “Misty glass” Vasiliev Andrew Team Voronezh.

Misty glass. Breathe on a cold glass surface so that water vapour condenses on it. Look at a white lamp through the misted glass and you will see coloured rings appear outside a central fuzzy white spot. Explain the phenomenon. 2

Objectives Conduct experimental investigation and observe the phenomenon under consideration. Explore vapor condensation on the glass. Describe the phenomenon theoretically. 3

Photo 4

Video 5

Vapor condensation on the glass. Vapor condenses on the glass when the temperature decreases below the dew point. The dew point is the water-to-air saturation temperature when the relative humidity is equal to 100%. 6

Experiment It was necessary to determine the size of the water droplets condensed on the glass surface. For this purpose I have used an optical microscope with the 100 x zoom. 7

Measurement of droplet size. Method 1. Choosing optimal zoom of microscope. 2. Making a photo of 1 mm division of a ruler. 3. Making a number of photos for various degrees of cleanness and temperatures of the glass. 4. Measuring the droplet size. 8

1 mm 9

Droplets Below there are the photos of the droplets formed on the window glass at temperature 22 OC. 10

30 mm 11

43 mm 12

50 mm 13

62 mm 14

70 mm 15

90 mm 16

Small droplets Droplets on the photo camera lens. Droplet size is about 2 -6 mm 20 mm. 18

Glass and plastic. Droplet size depends on wettability: ◦ If the surface is unwettable then droplets are smaller due to large wetting angle. Droplet form: ◦ On unwettable surface the droplet form is closer to spherical one. 19

Photos for various droplet sizes. ~ 15 mm ~ 70 mm ~ 8 mm Запасной 20

Misty glass. Colored rings are observed for the droplets < 10 mm For droplets > 10 mm we observe a central bright spot, a dark ring and one white bright ring. For droplets > 80 mm we observe one white bright ring. Therefore I suppose that the phenomenon has diffractional nature. 21

x d L

$Diffraction of light Bending of waves around small obstacles and the spreading out of$

Diffraction of light Bending of waves around small obstacles and the spreading out of waves past small opening. It is due to interference of light waves which came from different points. 23

$Diffraction of light If the droplets would form on the surface a regular lattice$

Diffraction of light If the droplets would form on the surface a regular lattice then the diffractional picture would not be colored rings but star-like patterns. 24

$Star-like diffraction picture on a regular lattice (organza). 25$

Star-like diffraction picture on a regular lattice (organza). 25

$Diffraction of light However, we have seen colored rings. This proves that positioning of$

Diffraction of light However, we have seen colored rings. This proves that positioning of droplets is random. Hence the Babinet principle is valid. It means that diffraction picture produced by a number of droplets is essentially the same as the one produced by one droplet. Book М. Борн, Э. Вольф «Основы оптики» . Москва «Наука» 1973 г. 26

$Diffraction of light Diffraction on a disk. Книга М. Борн, Э. Вольф «Основы оптики»$

Diffraction of light Diffraction on a disk. Книга М. Борн, Э. Вольф «Основы оптики» . Москва «Наука» 1973 г. 27

Experimental photos The lens of the photo camera. Ambient temperature ~ 0 OC. Increase of droplet size. 37

Photo 42

1 2 3 The width of matrix Deviation on monitor Width of monitor Deviation on matrix - Droplet size Matrix Monitor 43

Droplet size 44

$Diffraction of monochromatic light. 45$

Diffraction of monochromatic light. 45

$Diffraction on talc powder. Particle size ~ 20– 100. Random placing. 46$

Diffraction on talc powder. Particle size ~ 20– 100. Random placing. 46

$Diffraction of monochromatic light on talc powder. 49$

Diffraction of monochromatic light on talc powder. 49

Corona around Moon Halo A halo is an optical phenomenon produced by ice crystals creating colored or white arcs and spots in the sky. 50

Conclusion Droplet size depends on the temperature, cleanness, wettability of surface etc. Color rings are produced by the light diffraction on the round droplets of 520 size randomly scattered. 51

Thank you for attention! 52

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