1 / 20

Engineering Physics

Engineering Physics. b y Bhaskar Department of Physics. K L University. Lecture 07 (25 Aug) Interference in Thin Films. Newton Rings. Another method for viewing interference is to place a planoconvex lens (L) on top of a flat glass (G) surface.

jerry
Download Presentation

Engineering Physics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Engineering Physics by Bhaskar Department of Physics K L University

  2. Lecture 07 (25 Aug) Interference in Thin Films

  3. Newton Rings • Another method for viewing interference is to place a planoconvex lens (L) on top of a flat glass (G) surface. • The air film between the glass surfaces varies in thickness from zero at the point of contact to some thickness “d”. • A pattern of light and dark rings is observed. These rings are called Newton’s Rings. • Newton’s Rings can be used to test optical lenses.

  4. Newton Rings…..

  5. Newton Rings… • Ray 1 undergoes a phase change of 180 on reflection, whereas Ray 2 undergoes no phasechange R= radius of curvature of lens r=radius of Newton’s ring

  6. Newton Rings… How are these rings are formed? Let us consider a particular point which is at a distance of r from the point of contact of the lens with the glass plate. All points having the same thickness – Destructive Interference. Why are they circular? The locus of all the points from a circular dark ring with ‘r’ as radius. Centre is dark because of phase change during reflection at glass plate.

  7. Newton Rings… • For constructive interference • For destructive interference

  8. Newton Rings….. Conclusion:Fringe width decreases with the order of the fringe and fringes get closer with increases in their order. D16 -D9=2√Rλ ------------->7 Fringes D9-D4 = 2√Rλ -------------->5 fringes D4-D1= 2√Rλ ---------------->3 Fringes

  9. Newton Rings….. Out Comes: • Determination of wavelength of monochromatic source. • Determination of refractive index of liquid.

  10. D2 m D 2vs m Determination of wavelength of monochromatic source: Measure the radii or diameter of rings formed Measure the radius of curvature of the lens (R). Where l is the distance between two legs ofspherometer. h is height of convex lens. R = l²/6h+h/2 Dn , Dm are the diameters of the mth and nthdark rings λ =

  11. Spherometer

  12. Newton Rings… Determination of refractive index of liquid: Liquid

  13. lens lens liquid air glass plate glass plate Determination of refractive index ( µ ) of liquid = = 4(m-n) λ R µ

  14. Newton Rings… • For a air film between the plane convex lens and a flat glass • For a liquid medium (whose refractive index is to be measured) between the plane convex lens and a flat glass • Resultantly the RI of • liquid medium can be written as

  15. Primary Application's of Interferometer 1) Optical Testing : Surface Quality a) Flat Surfaces b) Spherical Surfaces c) Surface roughness 2) Direct phase measurements a) phase shifting b) phase stepping 3) Aligning very high quality lenses 4) Space applications a) Radio Astronomy b) Measuring light intensity c) used in retrieving images from telescope

  16. Newton Rings… In white light

  17. light :a wave leading to our future The end

  18. Problems In Newton’s ring experiment , the diameter of the 10th dark ring is 0.433cm . Find the wavelength of incident light, if the radius of curvature of the lens is 70cm . In Newton’s ring experiment , the diameter of the 5thdark ring was 0.3 cm and the diameter of 25th ring was 0.8 cm. If the radius of curvature of the plano convex lens is 100cm. Find the wavelength of light used.

More Related