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Pierścienie Newtona - Zestaw na Ławie Optycznej - typ: EXP200080

A very slightly convex lens is placed in contact with the flat surface  of a glass slide. It then forms an air wedge with
a curvilinear boundary  surface. If the device is illuminated with an incident light with  parallel rays, concentric interference rings are formed around the  contact point of the two surfaces. The distance between the interference  rings
is not constant since the air wedge boundary surface is  curvilinear. In this case we shall use a sighting device
for our  measurements. We can combine this device with a webcam to retrieve data  on a computer.
Pierścienie Newtona - Zestaw na Ławie Optycznej, typ: EXP200080

The Newton’s rings device yields rings in view of its rotational symmetry. Another difference is highlighted by the type
of reflections involved. Reflection is of the glass-air type on the spherical diopter of the lens, and of the air-glass type
on the mirror.

Newton’s rings are in this case observed
in transmission as the flat plate is transparent. The central ring is thus bright.


We illuminate at normal incidence, with
a monochromatic parallel beam of light, a large-radius convex flat lens placed on
a glass slide. Part of a ray is reflected on the glass-air interface  without phase change, while the other part passes through this  interface, and a fraction of this ray is reflected on the bottom slide.  As this ray is reflected by a more refractive medium, this reflection  produces a phase shift of π. These two reflected rays, of adjacent  amplitudes, interfere by yielding localised fringes (as for thin plate)  in the vicinity of the lens spherical surface. Let R be the radius of  curvature on the underside of the lens. In other words r = OI is the  distance between the ray and the optical axis of the system.

As r is far smaller than R, we obtain: e ≈ r2 / 2R. The optical path  difference is formulated as δ = 2e + λ / 2 = r² / R + λ / 2. As the  system accepts an axis of revolution, fringes are rings centred on this  axis. Dark rings are obtained when δ = (2k +1) λ / 2 or for 2e = r2 / R =  kλ. If the lens is in optical contact with the underside, the first  ring will be dark. The following rings (the optical path difference  increases by one wavelength between two rings) have radii proportional  to the square root of an integer.


»»Air wedge
»»Radius of curvature

  1. POF010112    Prismatic optical bench, 1 m x1
  2. POF010124    Optical rider x3
  3. POF010126    Optical rider with horizontal motion x1
  4. POD066061    Newton's rings device x1
  5. POD010030    Pedagogical webcam x1
  6. POD010057    Mercury spectral lamp,
    high pressure x1
  7. POD010056    Stand for spectral lamp x1
  8. POD010572    Green interference filter- 546 nm x1
  9. POD069440    Viewfinder x1
  10. POD061250    Dual condenser x1
  11. Computer is required for the webcam

Zestawy i Stanowiska Edukacyjne dla Uczelni Technicznych: Optyka - Pierścienie Newtona - Zestaw na Ławie Optycznej

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